I live in a small alcove (L-shaped) studio and while it's an obvious choice to put the bed in the alcove, my queen size bed barely fit and since I have no desire to go smaller than a queen I'm using it for my home office and dressing area.
I purchased and, using a jigsaw, cut down a wood countertop to fit the length of the wall (67 1/2") and then cut the depth down to 20". As you can see anything deeper would overwhelm this area.
I draped a linen gauze curtain from ABC Home to conceal what's under the desk, and had a glass top custom made by a local glass company. The curtain and glass aren't secured to the table, just delicately placed so I can remove the curtain to clean occasionally.
Doing this wasn't exactly less money than buying a desk, but that wasn't the point. The point was to have something that seamlessly fit the space as to not draw too much attention to itself. To have something that was functional for my needs and that fit my space.