Bunkbed play area?

[la79al]

So here's a question I don't know where else to ask.  The girls playroom is getting out of control.  They change what they want to play with everyday and rotating toys is not an option.  It's a smallish room, I think about 10'X12'.  I was thinking, we have a set of metal twin over twin bunkbeds sitting in the garage.  Would it be stupid of me to bring them inside, put them together in the playroom, put a piece on plywood on each bed and thus increase the girls play area?  I was thinking maybe put art supplies up on the top and the princess castle down on the bottom, plus we could put storage bins underneath.  The girls are 6.5 and 4.5 and sleep in bunk beds already so I wouldn't be worried about them climbing up.  I might want to do a little bit of work to the sides on the top, only because I'm paranoid. Ideally we would buy or have made a loft type thing but money is super tight and the playroom is really the last place we would be spending it if we had it.  

[NandaB]

If anything I would leave the mattress on top and maybe put up shelves on the wall for books so they have a reading/relaxing space. But I wouldn't want to sit/kneel on plywood to draw. That seems uncomfortable. It probably makes more sense to spend a little money on some plastic organizers so they have easy access to stuff and can put it away on their own