Treat the twin bed like a daybed and disguise the frame with pillows and a straight linen bed skirt. Use bolsters, European square pillows, regular bed pillows, round and triangular pillows. Cover them in mixed fabrics. Instead of a bulletin board over the bed, hang framed art or a colorful vintage poster that coordinates with the bedding. The bed skirt and the wall art create a visual tableau rather than a simple view of a bed.
Put a twin mattress on a platform that will provide storage, either with drawers or a lift-up panel under the mattress. Then make a headboard from a sheet of plywood covered with a photo mural on canvas. Photo murals are just enlarged photo canvases, easy to order at photo shops or online. The mural can be mounted to the wall or to the bed platform. This is a great way to let a teen dictate room decor. The photo selection drives the colors for the rest of the bedding, walls and rugs. You can even turn a couple of runner-up photos into pillow shams.
For a shared room, build or buy bed frames that line up end-to-end. Drawers under the bed frames provide storage and a closet along the opposite wall holds more toys and clothes, leaving the center of the floor as uncluttered play space. If the room isn't long enough for traditional twin bed frames, build shorter beds for young children and use blocks of cut foam for the mattresses.
A twin fit for a queen is simple to set up when you attach a headboard covered in luxurious fabric to the bed frame. Make a wood headboard frame, pad and cover it and tuft the fabric -- cotton velvet or Chinese embroidered silk are elegant. Attach it right to a plain bed frame, the kind that comes with a mattress and box spring set but has no headboard and foot board.