Cork board

I read that you can use cork board for diarama bases. So if I wanted to build a diarama with a crater hole would I just take about 6 pieces of cork board and cut a hole in each one then stack them? I'm not sure if that is how that works. Also how do you make grass for the diarama. Just one last question, is it better if you want to make a model barn with balsa wood or just by a plastic barn? The scale of my diarama is 1:35 and the size of the grass I want would be like if you didn't mow a yard in a long time like two weaks. So it would be around the middle of the tow on a 1:35 scale soldier.