Ya, Cmnash has it right! If you can put it on a backer they last a lot longer.
Your efforts look quite good PLS, no slouch at all!
Another great thing about cardstock is that you can print the same thing out a couple of times for pennies, then layer bits to give depth, like window and door frames or ledges, even whole walls with holes cut out for recessed windows. Can really help make buildings look less flat.
"I saw this in a cartoon once, but I'm pretty sure I can do it..."