i've also used plastic milk jugs when i need a template for a small piece. they're easy to cut and easy to clean.
you could also use cat litter jugs - not the large square ones with the (approx) 12" x 12" lids. i'm talking about the ones with the screw tops. the plastic is a bit thicker than the milk jugs, and there's a lot more area so you can make a larger template piece.
a bit off topic but a useful tip -
when i need to rough out a piece on paper first, i usually need a lot more than an 8 1/ 2 x 11 sheet of paper. often times i'd like a full scale drawing - and i'm sure i speak for most of us in that regard. i used to work for a contractor, so i'd bring home rolls of old blueprints. some sheets are 24" x 36 all the way up to (memory going........) 48 x 96??
anyway, you can probably get all you want from a construction contractor ( GC, roofing contractor, plumber, electrician, etc) or architectural firm.
if any of them want cash for their old blueprints - walk away. you can score them for free.