I use PCV plates 1-3mm thick. Its very good material. You can bend it, but it's still hard enough. Easy to glue and what is the most important for me- you are able to carve in it with silmple tools (like i did with the lines on the floor). Aaaand it's incredibly cheap
1m2 of 3mm plate is about 10 euro. More than enough for couple of projects.