IKEA makes DIY bedding options easy by providing standalone slats, so this trick could be a great option for the apartment dweller looking for portability. It's as easy as putting together two single-width Expedit shelving units, laying them parallel to each other on the floor, then laying the slats across them.
You can make the frame more permanent by fastening the slats to the shelves with either nails or screws, but it's not exactly required — I just wouldn't do any acrobatics on it until you do. Hit the link below to check out more details and images.
Expedit re-purposed as bed frame for maximum storage [IKEA Hackers]