Some tips on using this highly coplex tool:
The scenario editor can be a very powerful tool if it is used correctly. It lets you 
build scenarios that you can play or share with friends, it's even better for 
webmaster! =) However it takes time and patience to make a fun and yet, 
challenging scenario.

I would recomend that you play the game before you attempt to make a scenario,
even then be prepared to make a few mistakes on your first attempts. 'Cause you
aren't a master like Mr. Sawyer ;-)

Think Small (Really Small, Tiny Small)
On your first few scenarios, make a small park with only a park entrance and a 
bit of path, making sure that you have the path connect to the edge of the map.
This way you can go and play it to make sure that the park works, so you don't
spend hours on a huge park that doesn't work properly.

Think Simple (Shouldn't be hard ;-))
Make only land adjustments and outside scenery, this way you will still leave 
room for the player to think and create their own park, I'll almost bet that none of
you have played the "Real Parks" in the first one (if you plaed it at all) due to the
fact that they were already built, and had almost no room for improvement. So be
sure you don't take the fun out of your scenario by thinking and creating for the 
player.

Make the park entrance first.
By making the park entrance first you will establish where the guests will arrive.
Remembering that the path th the entrance must connect to the edge of the map,
You must place paths in the front and in the back of the entrance, but first place
the entrance then the paths on both sides, you then must mark where the guests
will appear on the path that leads to the front of the park entrance.

Establishing the Player-Owned Land Next. (The Hard Part)
While your doing this always keep this in mind:
1. The path coming form off the map to the park entrance should not be owned or
available for purchase by the player. The game will automatically set the route to be
non-purchasable (If you forget to do it).
2. The land owned is continuous, The best shapes for owned land ar circles, 
squares,and rectangles.
3. If a player can not buy more land in the park they should at least be able to buy
the construction rights to un-owned land so that seperate ares of owned land, can 
be connected.
Note: Any "Unusual" shaped parks, such as a "U" shaped park will confuse the 
guest and generat a low park rating.

Dont let 'em have it all (I'm guilty of this)
Let your players work their way through the scenario(s) you've made, to see all the
game has to offer at a gradual pace. If you give the player all the land on the biggest
map and all rides and attractions available at the start, they may be overwhelmed 
and feel that they have nothing to look forward to. A good scenario should challenge
the player. (I have broken all those rules with my "Flatland" Scenarios)

Test your Scenario on occasion.
As you are building the scenario test it on occasion to ensure that everything is
working properly and that it is as challenging as you wanted it to be and the most 
important thing is, is to make sure that it is fun, if it is fun for you it will, no doubt
be fun for your players. You should most definatly test it once your scenario has 
been completed, to ensure that the objectives you've set for that particular scenario
are in reason and aren't too hard (I know you hate it when you have to try to beat a
level several times before you acctually do)

To Save or Not to be Saved (That isn't the question)
As you know there is no Undo or Redo button in the game (Don't know why) so you
should save your landscapes often (every few min.) Just incase you make you 
landscape F.U.B.A.R. <-(Don't ask) Then you can go back and load the landscape
before you screwed it up completly.

The 6 Steps to building a hella good scenario:
There are images through out this section click on the thumbnails to enlarge them in a new window.
1. Select Objects
2. Edit Landscape
3. Invention Setup
4. Option Selection
5. Objective Selection
6. Save Scenario

Select Objects
 This is where you select all the objects that will and could appear in your scenario.
You can only select a certain number of objects in each catagory, and this number 
varies with object type, For example, you can select 128 ride types, but only 19 
scenery types, 1 park entrance style, and 1 water texture.

 The more items you use, the longer your scenario will take to load. The items with
the white check mark are the items that have been selected to be in your scenario
 The advanced button adds five more tabs to the selection. This allows you to 
select individual theme elements without having to select the full theme package.

Edit the Landscape
 Here is where you will be shaping the landscape to create the bulk of the visuals in 
your scenario. You won't be placing any rides in this part of the scenario, just the 
scenery. (To make a scenario with an active running park filled with rides and 
guests, you will need to use the "Convert saved game into scenario" feature located
in the toolbox menu on the main screen.)

 Sculpt the land as you wish. You can even use the mini-map window to paint larger
areas of land with different land tiles or mark owned land or land for sale. To move to
the next step you must have these elements in place: a path leading from the edge
of the map to the parks entrance(s), a set "guest appearance" marker(s) on the path
and land designated as "owned" by the player, that doesn't include the path or park
entrance but leads to it.

Invention Setup list
 When you are done creating the look of the scenario, you need to decide what 
inventions the player starts with as well as which ones the player must research.

 Sort out the "To Invent" list by dragging items into the sequence you want. Or you
can just click the "Random Shuffle" button to randomize the order in which 
inventions are discovered.

Options Selection
 This is the place where you decide what details of your scenario is. Click the tabs
to set the options.

Financial
 This is where you establish how much money the player starts out with, as well as
their initial loan, max. loan size (max is 5,000,000, and intrest rate. You can also
make marketing campaigns forbiden here.

Guest
 This is where you establish the amount of cash the guests have when they enter
the park on average (max is 100). You can also adjust initial behaviors and 
characteristics, including happieness, hunger, and thirst, also wheter guests prefer
more or less intense rides.

Park
 Here you can set the cost of land and construction rights, and decide whether it's a
"pay at the gate" park or a "pay per ride" park. You can also set things such as 
forbidding tree removal and/ or high construction.

Objective Selection
 Each scenario needs a goal that players must reach in order to complete the
scenario. You should always make it a reasonable as well as a fun goal to achive.
 The Objective screen is where you set scenario goals, climate , and descriptions.

Objective
 The objective drop-down menu contains a list of various scenario goals, such as the
number of guests or park value after a certain time period, or building roller coasters
of a certain length or excitement rating. Depending on the goal, you need to set 
additional parameters, such as number of guests, and a time period. These choices
appear below the Objective menu.

Climate
 This menu lets you select between a choice of four climate types in which the park
will be set.

Park Name
 This is the initial name of the park. Players will be able to change it once they start
the scenario. Click the Change button to enter a park name.

Scenario Name
 By default the scenario name is the same as the park name, however you can 
change the scenario name by simply hitting the Change button. It is the name that will
show up in the scenario screen.

Scenario Group
 Under this portion is where you chose the catagory of park (this is where you testing 
it comes in). There are 5 choices for you to pick from depending on how you felt the
challenge raing was: Beginner, Challenging, Expert, "Real" or other. This is the 
catagory in which the scenario will appear.

Park/ Scenario Details
 Here you need to enter a sequence or two to give the players an idea of what to look
forward to in the scenario. Click the Change button to enter a message.

Save you scenario
 Click the save scenario button in the lower right corner to save your scenario and
return to the main menu. your scenario will appear in the Scenario Selection screen
under whatever catagory you assigned it, unless you saved it somewhere else on your
computer.

Covert Saved Games to Scenarios
 Use this utility found in the main screen under the toolbox, to create scenarios from
saved games. This is the only way that you can make a scenario that includes 
previously built rides, and guests already in the park, and other components that you
can alter after playing the game.
 Click on Convert Saved Game to Scenario in the Tools menu and then choose a 
saved game from the list that opens. This opens the park in the background, you can
look at it, but you cannot edit it. What you can do though is set the goals oin the 
Objective Selection window.
 If you click the preserved rides button, you are given a list of all of the rides that are in
the park. Click on a ride name to put a checkmark next to it. Rides designated as 
preserved rides cannot be torn down or edited but the person playing the scenario.
 Click the Save Scenario button in the lower right corner to save your scenario and
return to the main menu. Your new scenario will appear in the Scenario Selection 
window under whatever catagory you've assigned it, unless you saved it somewhere 
else on your computer.