Looking good but a bit too tidy for mine (lol)
I have used loads of old drainpipe sections suspended with wire ties from the ceiling and walls along with different size branches from floor to ceiling and across from back to front and side to side.
Mine also enjoy sitting as high up as possible in the corners I just use old bits of plank across the corners held on with a couple of staples.
Perhaps you may get more ideas if you go to some of the older posts in pictures section. hers a link to one such post:-
http://super-chipmunks.co.uk/forum/index.php/topic,129.msg872.html#msg872As for the floor I would personally cover the flags in a mixture of compost and bark and lay some more pipes down for them to run through and hide in.