first of all is that illegal?

j/k
i got 16 plans for my whole school, they are giant! (1 : 50) now i have to messure the length, calculate them into meters and then back to the game (editor) length!
now my question: i started to build the map with the noter "texture" that means the whole map (as far i build) is invisible, now i have to add the textures, just to try out the map, but i have big problems to select every wall, door etc and then add the texture, so what is the best way to map?
i finished first floor, and it looks quite good in the editor, i gonna do it as they did it with HL2 i just insert an organge texture and play the map just to find some errors or bugs in the map!
Creatures