Here's just about the simplest design for a queen-size futon frame that we've ever seen. It's essentially three hinged pallets, two of which form the back of the couch during the day, and lie flat at night. Have your mattress on hand before cutting any parts, as they tend to vary a little in size. You'll also need to purchase a mattress with two ''hinges'' in it, rather that the version with a single long fold. A source for this is listed. This is basic carpentry that's well within the abilities of most woodworkers.

Approx: 6-1/4'' x58'' wide x 88'' long (when lying flat)