I usually make mine somewhat smaller, but it depends on the models you're using I guess... I only use humanoids (no orcs or such) and therefore I gave my town a bit of a human feel to it.. so my floors are 2" high (which makes it great for climbing and jumping down without restraint)
For measurements I just position a model in the doorway I'm about to build, and see how it fits, then I build the rest of the building from there on... (of course, now I have my buildings ready, I don't need to measure every time...