Well if you don't worry about pretty, I actually suggest a sheet of plywood, or cardboard((which would need replacing every so often when they rip through it, also a plus to entertain the buns XD)). Vinyl or any smooth floors will give no traction to buns and they will slid around and possibly flip over((believe me, my buns done it on my wood floors from trying to run, it's not pretty or fun for either of you)). And carpet they would/could eat, as well as plastic; neither of which are very good.
Plywood would give him traction as well as protecting the floor. It would be kind of ugly, though.