I assume you mean Murphy beds.
How often during the year are the four beds all used at the same time? Perhaps renting for these short periods would be more cost effective than purchasing lumber and all the necessary tools required to build four beds.
Switching to multi use furniture, such as trundle couches, or loft style beds, may be another option. Some examples are below.
I agree with Flipturn, storing 4 beds folded up against a wall will still take up space in the actual room floor plan, unless you want to have them fold up into the wall and covered by a door. That is a lot of work and skill involved. Plus do you want to look at the underside of 4 twin beds? I would opt to either rent beds of have blow up air matresses. Best to you.
Do you want Murphy beds?