Things to Consider Before Buying a New Bed

Decide the storage type first, because it changes the whole build. A plain bed is the cheapest and lightest. A box bed gives storage through small side or top flaps, usable for things you rarely need. A hydraulic bed lifts the entire mattress platform on gas pistons, opening the whole area in one motion — this is the only version where the space is genuinely usable week to week.
Fix the mattress size before the frame. 6x6.5 ft for a king, 5x6.5 ft for a queen, 3x6.5 ft for a single. Build the frame to the mattress, not the other way round, or you will be hunting for a non-standard mattress for years.
Check the piston rating on a hydraulic bed. The pistons must be rated for the weight of your mattress; an under-rated piston will not hold the platform up, which is both a nuisance and a hazard. Ask for the rating in writing.
Measure the room, not just the bed. You want walking space on at least one long side, and enough clearance for the wardrobe shutters to open fully.
Lastly, plan the headboard with the wall. A headboard, back panelling and side tables built as one composition costs little more than the bed alone and finishes the room.