Wanted: a small piece of roofing felt

Anyone know where I might find a very small (like, 3' x 3') piece of roofing felt/tar paper? I can't justify buying a roll, which is like 100' long or something, when I only need 3'. I'm thinking of calling some roofing companies to see if they might have scraps that they just throw away, or walking around my neighborhood and looking for roofing projects-in-progress...

In other news, the library now (as of today) has a ceiling and a floor! That means all the large pieces are now attached to one another! Very exciting!

Here it is on its side, weighted with a cinderblock while the wood glue dries:

The black box on the bottom is the fireplace, shown here with the symbolic king-post marker that's in the middle of the floor:

And the little round thing on the left in the first picture above is the symbolic top of the king-post, shown here next to the ceiling trapdoor into the garret:

So it's coming along. Now I have to figure out the door (the functional one that you'll use to access the books) and make one, then make the platform that it will all attach to, and the woodshed, and finish/attach the chimney, and make a stand to put it on, and shingle it, and paint the inside, and complete the various decorative bits.... Yeah, it'll take a little while longer...