Excellent. If you get something going, others could contribute and this would be very useful for new people. (Grimber wrote a fantastic tutorial for a FPS but it was in C-Script and too difficult to translate)
I assume you only have Lite-C ? Someone could contribute a small level I am sure.
I was thinking something simple say, about 3 rooms with maybe a door, stairs etc. People could add extra rooms, levels, textures etc in their own time.
I looked though the AUM Magazine and I found plenty of simple games like Moorhuhn (shooting poor birds) but not an expandable FPS.