Begin by developing a plan. This does not need to be a complex blueprint, simply a drawing of how you want the space to be set up. How high do you want the bed? How big is the bed? What will the general layout be? This will help you determine the supplies you need and direction when actually assembling the loft. It is a good idea to check with the dormitory to see if there are any requirements that may be in place for lofted beds before making the plan. You would hate to make your plan, purchase all the supplies and assemble the loft only to find out it does not fit the dorm's codes.
Purchase all necessary supplies. Based on your design, you should be able to calculate how much lumber you will need. In the following example you will need these supplies for a standard twin size bed: seven 2x6s at least 7 feet in length, five 2x4s at least 7 feet in length, and one 3/4 inch piece of plywood 4x8. You will also need to purchase the necessary hardware including at least forty 3-inch wood screws, at least a dozen 1 5/8 inch wood screws, and eight 3/4 x 3 inch bolts with nuts and washers.
Building the loft portion for the bed is fairly simple. You will just build a box using the 2x6s and the plywood. A twin bed's dimensions are usually 38 inches x 76 inches but you should measure the bed to make sure. If this is the case then cut two of the 2x6s into 78 inch sections. Cut another 2x6 into two sections, 37 inches long. When you assemble the box, the long pieces will overlap the short pieces at each corner. What you end up with is a box that measures 40 inches by 78 inches and is five and one half inches high. Use the 3-inch wood screws to connect the 2x6s. Cut the plywood to fit on top of this box. Use the 1 5/8 inch screws to attach the plywood to the box frame.
Position two of the remaining 2x6s so that the outer edges are parallel and spaced 78 inches apart from each other. It is easiest if you simply lay them on the floor for this so the wide part of the boards are facing up and down. Measure the boards and mark on each how high you want the bed to be off the ground. In this case measure 48 inches from the bottom of each board and make your mark. Take the box frame and tilt it up and place on the 2x6s so that the bottom of the box frame sits on the mark you just made. Make sure the 2x6 "legs" are straight with each other. Using the electric drill, drill two 1/2 inch holes through the box frame and into and through each leg. Using the 3/4 inch x 3 inch bolts attach the box frame to the legs. Repeat for the remaining two legs.
Place the loft upright so the legs are on the ground and the loft box, attached to the legs, will be up in the air. It will look like it should when completed but it is not ready to be slept on just yet. The loft will probably sway back and forth so you will want to use the 2x4s to create support pieces, and a ladder at the same time. Cut the 2x4s into six pieces, 40 inches long. Starting about 18 inches off the ground, attach one 2x4 to the legs across the end of the bed using the 3 inch wood screws. Repeat with the second and third pieces in 12 inch intervals. Repeat on the other end. On the part of the bed that will face the wall you will want to attach a 2x4 to the two legs about 30 inches from the floor. These support pieces should prevent the bed from swaying in any direction. You should now be ready to get a good night's sleep in your lofted bed.