I have seen several builds that started with lexan for the upper and lower hull. Styrene can be used for detail parts but the lexan is heat, flex, and damage resistant. You can mill it for curved bits, and cut it clean on a table saw. My future M10 build will be lexan upper hull on a sherman lower assembly. Check out this pic of a Lexan KV1 done by a member of SCAT.

http://web.mac.com/ksoc/iWeb/S.C.A.T...0Projects.html