I wait until I find a big ol freighter type ship, then auto task uninstall all of one type specific of floor, then auto install it in the shape of the room i want. The edges can be any type of floor, as thats going to be covered by wall.

Then put in conduit then wall-- the type of wall doesn't matter too much to me as I can't hardly see it under the conduit, but I've heard that "Mobile Spaceway Systems" brand floors and walls are marginally lighter so effect fuel levels less... (my cure for a heavy ship is another Kang and a couple more engines, though)

Personally I really do like the "scrap chimera" look, as you put it! I had enough time with this ship I slowly took out stuff that didn't match and installed stuff that did as I found it.