I've done various caging wire, premade more bar floors, and various solid floors. I like the metal conduit bar floor idea. I was trying to figure out something similar for guinea pigs that in other countries are kept on curved bamboo floor slats but I can't get equivalent wood products in the US. Guinea pigs get sore feet a lot more easily on wire but it has potential for larger rabbit cages over what thin wire I can get locally.
For solid floors or really any wood item you can solve a lot of problems with a can of rustoleum enamel. Completely nontoxic once fully dry, waterproof, and wipes clean like plastic. The myriad of polyurethanes work too but some may have toxic ingredients. I've only found definitely safe marine polyurethane for boats once around here. The enamel is in practically any hardware store and cheap so I have coated a lot of wood bases for guinea pigs, chickens, rabbits, gerbils, degus, and reptiles in it. Just don't scrape it off with rock or metal edges and it lasts 5-10 years or more. It can also be repainted as needed. The only thing with small mammals is you sometimes have to protect the edge of the wood or they will keep chewing off your seal and it's probably not as safe to ingest as it is to live on. We ran piano hinge aka continuous hinges down the edges of things like degu cages so the wood is mostly impervious to chewing. That way I can build practically any shape or size I want out of solid wood with the only remaining downside of the wood being weight. Far more work and limitations to rely on cutting metal for every part of a cage.
