Pull-out or trundle beds are convenient when you want to have guests visit your home. The pull-out bed is stowed away when it isn't needed, so it's a space-saving alternative to a whole extra bed. It's a worthwhile choice for small spaces and for childrens' bedrooms. It's possible to buy beds that come with a trundle, but if you have an existing bed that you want to make a trundle for, you can build one yourself.
Measure the bed you are making the trundle for to ensure the trundle will fit snugly underneath. Measure the overall height of the space under the bed, the overall distance between the legs of the bed, and the width of the bed. These measurements also determine what size materials to use. If you have 8 inches of clearance, you will use 1-by-8 lumber; if you have 10 inches, you can use 1-by-10 lumber.
Subtract 2 inches from the overall height to determine the greatest possible height for your trundle. Subtract a 1/2 inch from the distance measurement to determine the greatest possible length of the trundle.
Cut the plywood equal to the length and width of the measurements for your trundle. Cut the lumber into four pieces to fit snugly around the plywood. Attach the end pieces of the lumber to either end of the bed, using the 2-inch screws. Attach so that the end pieces extend 2 inches from the bottom of the plywood.
Attach the sides of the trundle, using the 2-inch screws and leaving 2 inches of clearance from the bottom of the plywood. Screw the sides into the end pieces as well as to the plywood.
Attach caster wheels. These make the trundle easy to pull out and will help prevent the frame from sagging. Use screws to add one wheel to each corner of the trundle, and two in the centre of the trundle.
Fill screw holes with wood putty. Sand and finish trundle as desired.
For convenience, stay close to the measurements for a standard trundle mattress: 75 by 39 inches. That way, you'll be able to outfit your trundle with a standard twin mattress, twin sheets, and so on.