Basil doesn't mind a plastic bottom tray, but we find it a bit skiddy for him, especially when he gets really excited. You could perhaps cover it with something less slippery, maybe and old blanket or piece of carpet. Are you going to litter train him, because that will make life so much easier for you? These are the area sizes Basil can use, dog crate approx 120cm x 60cm x 60cm, Conservatory 240cm x240cm, Garden Shed/Playhouse 180cm x 120cm, Garden run 120cm x 120cm but we are thinking of extending this at some point with some of the 'Runaround' equipment. You can view this site at http://www.runaround.co.uk/runaround/Home.html
I think it looks great!
I've put a blanket down for him just in case, he seems to find it quite comfy I am litter training him, started already! I thought that'd make it easier for when I start properly letting him run around, so he doesn't end up going all over my room.
Thanks for all the help everybody, I think I've got him a nice set up for now, until I can extend it fully.