Sheet Styrene. Clear for the windows, opaque for the doors. It cuts with an Xacto knife, or sissors and glues with styrene cement. Interior doors ought to have glass windows in them. Hobby shops sell small (6*8 inch) pieces of styrene. You might be able to scrounge some scraps off your local glass and plastic shop.
David Starr www.newsnorthwoods.blogspot.com