Creating a Level
From Gothongs Wiki
This is a tutorial that lets you create a very basic level with no scripted events. This level sets up a spawning spot, spawns monsters and adds an exit.
Step 1: Build your level
This is not something I can help much with. I am sure there are tutorials that teach you how to use the SL building tools. But here are a few suggestions:
Create a 10x10x0.5 prim as a base, and build everything 10m above it. It reduces the chance of you spawning the level on top of somebody. Here is a basic setup with a root prim "anchor" and a platform for players to walk on.
Build your level and make sure that the "anchor" remains the root prim by linking it last.