Finally got all the supplies together to make my kitty cube. I used the aforementioned metal wire modular kit but only used 1 cube (5 pieces). I used thick cardboard cut to fit in the bottom, wrapped it in a puppy pad, put it inside a plastic bag, sealed it up, put 1/4" foam padding over the top & added another puppy pad before upholstering it in felt. Outside of the cubby is felt. Inside is microfiber. I hand-sewed it bc my sewing machine wouldn't cooperate. I sewed 3 sides for each of the panels (felt sewn to microfiber). I had only secured the metal wire pieces at the bottom so I was able to slide the panels over (with 1/4" foam on the inner side for padding). Secured them at the bottom but left room for zip ties to secure the sides & back to the bottom more efficiently.
Poked holes for zip ties in higher parts & zip-tied on the top. Then I used plastic grid from a crappy "washable" HVAC filter that was garbage. I kept he plastic just in case though & it paid off. Hardest part of the entire project was cutting it. Jigsaw didnt' want to do it (wrong blade), Dremel was over at friend's house, Matrix ran out of battery & friend still has the charger. I ended up using wire strippers to make the plastic small enough to cut w/ scissors. I added the foam & taped it together. Was running low on felt so I used scraps to cover the front. Looks like Frankenstein's monster.
I only secured the front w/ 2 zip ties in the middle but sewed the rest of it on to the front by hand.
Got 1" foam for the kitty cushion. Upholstered one side in plush microfiber & the other in sherpa fleece. I added cheap shoelaces to tether it inside in case they get rowdy (although it fits very snugly). I hid the ties behind some of the fabric.
I just need to do some touch-up sewing & hang it up in their cage. Trying to figure out the best way to secure it so that if the cage ever needs to be taken apart, it still can be. I was going to use zip ties, but those are hard to remove & I need something sturdy but removable.
Wire pieces put together (sans top)
Upholstered with top attached
With front in place
Cushion
Finished cubby