G.B.
I can't read a question about bunk beds and not be very sad. I always thought they were pretty awesome for putting multiple kids in a smaller room but I have to tell you why I worry about bunk beds. My best friend from 7th grade into adulthood had a son who lost his balance and fell off the top bunk and he died, he just hit his head, it was a very simple injury, but he died. he was not rough housing, wrestling, anything. They are very dangerous and I always want to mention this to parents who may not have used them before because they can't possible know this might happen. He was in elementary school so he wasn't a little bitty kid either. Just please consider other options if you can.
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This may be the bed set the previous poster was talking about,
http://www.roomstogokids.com/index.cfm?fuseaction=ktg.sho...
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Here's another idea:
http://www.thefurniture.com/store/ASHL-SD-MSTL-TWIN-BDRM-...
If you were looking to do twin beds this shape would be ideal. It takes up 2 walls and leaves the center of the room open. You might be able to do this shape with two doubles but leave a gap in between the 2 headboards/beds where the girls can go into the square area and have a playhouse or toy area. You could get book shelves and put the back of them against their headboards and then they could have a little reading area with some bean bags and all their toys neat and sort of out of sight.