The bunk bed units are custom built in our cabinet shop. The designs very based on room layout and mattress sizes.

Thank you! I understand but what construction or support is used under the bottom beds and how was the top bunks constructed to give support? Thank you

It needs to have a cleat like a traditional bed frame with slats or have full load bearing on a ledger that is fasten to wall or cabinet box (use screws and glue). Substitute the box spring for a sheet of 3/4" plywood again make sure you have full bearing underneath. This also helps keeping the top low profile because sometimes headroom is an issue.