Nice design!
Carpet isn't really the best for a rabbit hutch or condo because unless your rabbit is incredibly neat it is bound to get dirty. I'd suggest using linoleum, which is a roll of vinyl flooring. I got a roll of about 8x1.5m for $30 as an off cut from a flooring company. It works great and is easy to install you just cut it to the right size and glue it onto the wood.
Other alternatives is vinyl tiles, which are made of the same material as linoleum but are cut usually into squares of 30x30cm. You can probably find a pack of 5 of these for around $5 at a local hardware shop. They usually have a sticky back you can peel off to stick to the wood. The only problem with these is the sizing, if the platform is bigger than 30x30 you'll need to use more tiles which means that there will be gaps between them and water/pee will seep through and get to the wood.
The third alternative is tiles. I'm not a big fan of tiles because they're mostly slippery so the rabbit could hurt itself when running on it, and also the grout between the tiles can soak up water and go gross. Also tiles are incredibly heavy so it makes removing them difficult and also you will need a lot of support to hold up all of the tiles.
Hope this helped! If you have any questions just ask! Good luck!