A tropical rainforest, eh? I like it. If you were to make one, though, I would suggest making the beginning-of-the-game forest be a rainforest (obviously!). But what might not be so obvious is how to map it so it's not just a forest with a cool name. Here are some tips:
1. There should be a main path, but a good mapper always knows the devil is in the detail. Add breaks in the trees, shrubs along the path, and plenty of grass. Also, debris such as toppled trees and vine tiles could go a long way in adding feeling to your creation.
2. Mud. If I've learned anything from traversing the rainforest, it's that there's never enough of the stuff. You may be able to deviate off the main path, sure, but where will it take you? Right into a puddle of mud, of course!
3. The place should be, above everything except functionality, natural. A map with a straight path and huge plots of solid grass is a boring map. Put in trees in the way, and most definitely do not make the path through the rainforest span from end to end. It should break up, then pick back up again. Also, one of the simplest tricks to make a map more natural is just to take out patches of grass. Instead of a solid patch, randomly replace tiles at certain points with regular ground or dirt.