There is one map like that already. Half of the map is covered in some strange colored stuff and it is the alien starting location. Called minetest if I'm not mistaken. The map is somewhat OK although the alien base causes too much slow down.
first of all, that map is old and this is about aliens the movie
second of all when it slows down its called LAG!!
third you have a slow computer probably because i have mac G4 and i dont lag there :evil: :evil:
First, when it slows down, it's called slow down, it's called a badly optimised map, it's called a FPS drop, but it is NOT called lag.
Seconds, every single player that went to the alien base ( yeah I know, this rules out more than half the human team ) will tell you that the game slows down when playing in there or in the tunnels near the base.
I can only say that you either used the wrong map, used a special "for you only" optimised verion, played in an completly empty server with cg_maxfps 10 or are telling lies.