We have three bedrooms, and (soon to be) 3 kids.
Me and OH share the middle sized room, and the kids have a bunk bed in the biggest room. The smallest room, is only really a box room, so will MAYBE put lo in there when he has stopped sleeping in our room, but will probably put his cot in the biggest room once hes about 1 yrs old tbh. The biggest room is quite big, so could easily fit him in, and put all the kids toys in the box room, so they have a kind of play room.
Also, the kids bunk bed is a triple bunk, where the bottom bunk is adouble bed, so once baby is out of a cot, he will probably go in the big bed with my middle child. Were lucky that they're all boys, or it could get really complicated though.
At first I felt mean making them share a room, but tbh, I wouldnt have it any other way now. I love listening to them playing together at night and in the morning. They keep each other entertained, and I think if I split them up now, they would just keep going back to each other anyway. MY eldest is nearly 6 and my youngest (at the minute) is 2 and a half, but they still play really well. It also helps that they have the biggest room, because me and OH dont need any floor space, we dont need that big room. And its great for them to play, instead of being cramped up, just because we want a big room.