Seriously, read the mapping guidelines. Draw some pictures. Make a simple room. Give it some nice, fitted textures. Give it some lighting. Then start an NS map. If you need help doing that FIRST try searching the Mapping Forum for an already existing thread on it.
Once you've done that, or at least made a decent attempt at doing it, you can be sure not to get any begrudging comments from me. But until then I'm not going to give you any more help. Everyone's new to mapping at some point, you just have to persevere and teach yourself. You really don't need ideas fed to you like a baby, just beleive in yourself and give it a go...
P.S. Welcome to the forums
P.P.S. If you get bored of your current idea
have a look at this. In one of my posts I said something about the original idea for the map that got scrapped. Other than that, no more freebies!