Hi , have a close look at the food trays used to sell meat , fish, cheese etc . Once washed out they make very handy temporary trays for assembled parts , but some are made from styrene plastic , I found out by accident a splatter of glue and hey presto a new free source of alternative coloured plastic sheets . I am speaking of here in the UK but it must be the same in other countries , so see what is out there cheers ian

Yes, those sheets I'm using for building houses and even a bunker. Can be covered easily with plaster or paper and then you can paint them how you like.