I don't think anyone of the mappers had Blueprints, but at least for the classic maps, some used the GoldeneyesetupEditor to get some size References.
The rest can be done simply by running the map on console or emulator and get some reference pics of the Architecture.
TBH, i did a rought bsp layout of stack from scratch without using a single reference, just out of my memory. Sure it's not 1:1 in scale, but this was not neccessary coz it wasn't planned as a map for GES anyway.
