Let your imagination run wild, I guess I think sometimes mine are just as happy with a cardboard box. They have balls, willow chews, seagrass toys, carrot cottages etc. Levels and hiding places are good as well as tunnels.
With regards to the actual room, we have used Lino on almost the entire floor (as we have a carpet chewer / digger) and a large mat covering the rest. We have used a divided up playpen to protect the skirting boards. The rabbits have a cage in there, but it's always open and has their litter trays and hay in.
The room is always messy lol. They do use the litter trays but there's always lots of random poos everywhere! It's my daughters bedroom, but she has a cabin bed with desk so they have lots of room. They've started going in the garden in the daytime now the weather is nicer.
I guess the keys things are plenty of enrichment, places to hide if they want to, a food and hay area and for the room to be bunny proof.
Good luck x