Imagine a center island map built by Newton or whatever, then put 4-5 smaller islands in a wagon wheel type layout that are mostly flat. The idea is you and another person have to create the best island out of all of the islands! Only 2 people per island. Now i'm sure Roy's post about credentials will suffice for these credentials but I will put my own for the sake of convenience.
Rules!
1. You can only build on your island, you can expand a little as long as it does not interfere with any other islands.

2. You cannot hinder any other island! No messing with their builds, but you are allowed to look at them for inspiration if you need it.

3. You do NOT have to be realistic! You can be crazy AS LONG AS it makes sense!

4. NO Roller-coaster can have an Extreme or Ultra Extreme intensity or nausea rating! (10 is the max that will be acceptable) Every coaster must be able to be ridden without the use of cheats.

That's all I can think of when it comes to rules. 

Each Category has a max score of 10 points! so 10/10 is your highest possible score per category. Categories are not limited to just roller-coasters, The layout and more will be considered. Max possible total score is 50

1.  Layout of paths: I understand that guests are not the brightest, but try to be somewhat neat with your path layout. I recommend that you don't use double wide paths but they are allowed.

2. Ride Variety: Don't build just roller-coasters! Guests love other rides too, so try to have a good variety of rides!

3. Roller Coasters: Be creative with your coasters! You don't have to be realistic, as long as they don't have an Extreme or Ultra Extreme Intensity! Remember that 10 is the max acceptable intensity rating, anything above that disqualifies the roller coaster entirely! 

4. General Theming : Try to be VERY creative! Do something that hasn't been done before, or if a theme has been done, throw your own twist in there to make it truly unique! This includes Rides, Roller-coasters, and anything on the island.

5. Functionality: Yes your island has to be able to support and manage guests ON ITS OWN! Meaning you must have: Food stalls, drink stalls, restrooms, information kiosks, first-aid rooms, benches, trash cans, and any other guest requirements! Staff will be provided so you don't have to worry about that.

The team with the highest score wins! if that wasn't already clear. Some other things to note is some cheats will be enabled such as: No breakdowns/brake failures, plant aging, chain hills on all track pieces, and staff that moves really fast. In short all of the cheats that are enabled on normal day to day server use. You can ask an admin or staff member to disable clearance checks and anything else you need.

That's all that I can think of. Just remember to have fun! and its not about who won, it's about how much you had fun creating your own little island!