I too would like to know if they are custom. They look like built ins

Did you paint or stain the bunk beds?

We painted them but you could stain them as well. If you paint them you can use birch plywood and poplar trim. If you stain them you would use maple, cherry or oak.

How big is this room that it accommodated these bunks so well?

Please research the safety requirements for bunks and appropriate ages for use. I don't think the top bunks look safe for children. They are great looking but should be safe for the ages that will be sleeping there.