outdoor enclosure ideas? need help

We've got a huge 18x50 enclosure built. It's roughly about 900 sq ft. We built it about 5 yrs ago and have had nonstop problems. We are now at a point where we can renovate/update it. The ground is nothing but grass and dirt so it's always messy. The roof is just wire (except for an enclosed end) so the rain doesn't help the mess and the snow is always so heavy on it. Last year it actually collapsed part of the wire and 4 cats escaped but I got to them in time to get them back in and we patched the wire. We want a solid surface over the whole thing just to be safe. So questions:
1) ideas for ground cover? Right now it looks so trashy with just the dirt and patches of grass. We want something affordable considering how big it is and something more sanitary as well as decent looking
2) cheap yet decent looking ideas for a roof? been wondering about fiberglass like greenhouses have. Yes or no? Other ideas?
3) cheap and better way to go about litter? right now they use it all over even in their enclosed end. It is so hard to get off the ground. Ideas about how to set up a litter area that's affordable? Maybe good alternatives to commercial litter?

There's 50 cats total. Thanks so much guys!! Also it's late and I'm exhausted so if I've forgotten to include anything you need to know just mention and I'll answer/explain. Thanks!

Wow, it sounds beautiful! What lucky cats.

My enclosure is 15' x 40'. The whole thing is a wooden frame, like a pole barn, but it has fence wire for the walls and roof. I put a small, barn shaped chicken coop inside, which is where the potty is. I also installed a sandpit outside. They have a cedar cat tree, a rabbit hutch, a cedar potting table and a cedar dog house, too.

I thought about covering the ground with the gravel they use in children's playgrounds. They also have shredded tire mulch. The only drawback to either of those is that my enclosure in under trees and I know I would be out there blowing leaves out and weeding. Otherwise, nature will take over and we'd be in the same fix.

I'm still thinking about it but the maintenance seems too much. Right now, I go through it with a weed wacker once a month. I also put down straw in some muddy areas, although they tend to use that as a potty, too, so I limit that.

I would be worried about roofing over such a large surface. Snow and weather could compromise the whole enclosure. Maybe instead of a roof, you can build a small building inside (or attached to one end to leave the square footage inside the enclosure. My guys sleep in the nest cubbies in the chicken coop. The coop is raised off the ground and I also have pallets under it where they lounge.

I got the wire fencing from Lowes. It is powder coated, with 1" x 3" spaces.

I might suggest, that with 50 cats, you might want to consider making it bigger, or dividing it in two. Also, build in as much vertical space (shelves or trees designed for outdoor use) as possible. The uprights on my enclosure are three feet apart, so I am able to put shelving up. (Haven't done that yet; it is my spring project). This will help increase the territory each cat has.

Thanks!! Unfortunately we don't have a way to expand the enclosure but we've decided to convert our old 10.5x10.5 shed into a huge cat house. We've got to renovate it a little first but when we're done it'll be decked out. Plus it's already been wired so we can have lights and a heater/fan in there depending on the weather. As for the enclosure we're going to attempt to build a canopy/carport type structure that will run the length of the enclosure to protect it from rain/snow. And for the ground, we're still working on it, but we're leaning towards a variety between fake grass, pavers, mulch, gravel, etc. I read last night that cats love that kind of floor in an enclosure. And we're going to work on ramps, walks, shelves, etc.

With the shed, you will have added another 100 plus square feet, so that's great. The pavers are a great idea - my enclosure is too hilly for that, although I do have a paved section the cat tree sits on.

I think the carport/canopy will work, too, as it will keep the snow out but not collapse under the weight. Good thinking!