If you've any indoor space you can get really creative. My ferrets used to live in a TV cabinet with cages tacked on the sides. Dog has a wardrobe.
Pallets are probably your best bet - even if not free, they're very cheap, solid, etc.
I sometimes think we're a bit fixated on small sheds for chicken houses -
There was a house in the John Seymour book; it was bits of pipe, tied into a frame, covered in chicken wire, old feed bags for and held on with more chicken wire.
Alternatively, if you might have little runs used for broody coops or chicks - How about one of these, covered over with plastic, up on bricks with either a mesh wire floor or something?