When I was building bird houses, I too would buy larger stock and cut it
down to size. Most of what I used I found by dumpster diving. I have built
about 50 bird houses that cost me nothing but glue and time. Sold most of
them, too! Allowed me to buy more tools!!!!!
Once I found a sheet of 1/16 black plastic, I cut that down to look like
shingles , that bird house adorns our yard. My wife decided it looked to
much like our own house to sell!