Set two 1 1/2-by-3 1/2-by-96-inch boards on the work surface. Arrange them parallel to each other and standing on their long, thin sides. Slide two 1 1/2-by-3 1/2-by-45-inch boards in between the long boards, perpendicular to them and flush with each end of the long boards so that the four boards form a rectangular frame.
Adjust the corners so they are even and drill two holes through the side of the long board and into the end of the short board at each corner. Drill 4-inch wood screws through these holes to attach the boards.
Place a 3/4-by-48-by-96-inch plywood sheet on top of the rectangular frame and adjust the plywood so that it is evenly spaced around the outside edges of the frame.
Pre-drill holes down through the top of the plywood and into the frame every 12 inches around the plywood. Attach the plywood to the frame with 4-inch screws placed in each hole.
Drill a hole in each corner of the bed, directly through a long board. Tighten an eyehook in each hole, using a screw passed through the eyehook to help rotate it if necessary. Stop rotating when the head of the eyehook reaches the wood surface, repeating to finish the four corners.
Find the joists or beams in the ceiling using the stud finder. Drill a hole directly into a joist or beam above each corner of the bed where you want the bed positioned.
Insert an eyehook in each hole and tighten fully. Open a 1-inch carabiner and slide it through the eyehook. Attach the end of a length of 250-pound tested chain to the carabiner and tighten the carabiner to lock it.
Attach a carabiner to each eyehook in the bed and pass the carabiner through the appropriate link in the chain hanging from the ceiling. Repeat for all corners and adjust as necessary. Lock the bed carabiners the platform is level.