Yeah, I'm having a hard time interpreting the drawing as well. It looks like you at least have a plan for how to go about making the map, though, and as long as you understand it, that's all that really matters.
Before you start making the map, though, I would suggest that you grab the tools and learn how to use them. It's always good to make a test/learning map before you attempt to make a real map, so you don't spend a bunch of time on a major undertaking just to have to scrap the whole thing because it's too much of a mess to clean up. Figure out how to make brushes, align textures, add lights, add entities, etc., so you'll be ready when you work on a real map.
Grab the build 15 BSP pack and start experimenting. Make something simple and learn. Make all of the things you plan to put in your full map and post the test map here so we can give some feedback on how to improve your methods before you make the full map.
