I semi-deep litter mine, using straw, I clean it out (me, a gripe and a quad-bike trailer, it's a day's very hard work
) every 2-3 months.
The straw on top stays pleasant and dry, I keep adding to it over the weeks. The stuff underneath is smelly and awful but you only find that out when you clean out.
I put mine in the corner of a field, let it rot down and then use it in flowerbeds.
I'd certainly put down paving slabs, rats will burrow under them and in due course you may need to lift them and re-do them. If you can put them onto 20mm chippings or bigger, that will both improve drainage and make it harder for digging rats.