Texturing help (Radiant and MBuilder)

[HDL_CinC_Dragon]

ok, my map is made out, i wanna texture it.
My map is simple, 4 sided brush (very large) that i hollowed out. i have four 8 sided brushes serving as tunnels (hollowed out, caps taken off) that create a + like thing inside the box, they DO NOT over lap eachother but they do meet. (i may add watch towers but thats later) I prefer having the ground be grass and the tunnels metal.


*An idea for advanced mappers*
Is it possible to make a search light replace an MG have the same basic thing except instead of a barage of lead make it a light, kind of like in Single Player.