You can make a cheap desk from materials found around a home. One way to do so is to use filing cabinets or shelving units as the supports for the desk, and doors or other long pieces of wood for the desktop. Apart from price, one of the benefits to making your own desk is that you can customise the desk to your specific needs and space. You don't have to worry that customising it will reduce its value, as it might with manufactured furniture.
Find a piece of wood or synthetic material suitable for use as a desktop. The desktop should be long enough to provide ample working space and strong enough to bear the weight of a computer and additional office accessories such as a printer or fax machine. Old doors or synthetic countertops make excellent desktops.
Locate two supports for your desktop. You can use old filing cabinets, shelving units, kitchen cupboards and vanities to support a desk. Supports should be the same height. If you only find one suitable support and you have woodworking skills, use the saw to make a support for the other side by cutting two-by-fours or other construction grade lumber and assembling them into a sturdy support that is the same height as your other support. Brace a homemade desk support with other pieces of wood.
Place the desktop on the two supports and line it up so all the components of the desk are in their desired positions. Supports should hold the four corners of the desktop evenly so the desktop does not wobble. Set the carpenter's level on top of the desk to make sure that the supports are balanced. If they are not perfectly level, add height to the supports as required. You can use scrap wood as wedges under the supports for small adjustments in height.
Attach the pieces together. Drill holes for the screws, drilling up through the top of open supports such as shelving units and into the desktop. Don't let the holes break the surface of the desktop, as this can scratch paper and other items in the future. For solid supports, you need to drill your holes down through the top of the desk and into the support.
Attach all sections firmly by inserting screws into the pre-drilled holes and tightening them. Your desk shouldn't wiggle, wobble or sway when you put pressure on it.
Use washers with screws to prevent the screws from sinking into wood over time.
Choose support objects carefully and be sure they can support a desk. If an object bends or gives way when pressed upon from above, this is an indication it is not an appropriate desk support. Test possible supports by placing heavy objects on them to determine their effectiveness.