Balsa wood is a unique material, as it's light and cheap but also fairly strong for its weight and size. It's used in a number of crafting projects, model-building and competitions for making balsa structures to bear weight. While making a balsa wood structure is simple enough, making them strong enough to stand under their own weight or to bear weight can be challenging.
Design a structure that will meet your needs. Draw a rough draft, taking the needs of you structure into account. Begin with an outline, and then design the support system. Include multiple angles of the structure to calculate. See the photos in Resources for further inspiration.
Calculate the scale and height of your structure, based on the amount of balsa wood you have available. You can calculate the scale by measuring the lines of your drawing on paper, and adding up the lengths. Then setting that as a ratio against the length of stock wood you have and, finally, simplifying that ratio. You can then use that ratio to estimate the lengths of all the pieces in your diagram.
Measure the length of the base pieces on your structure, then mark those lengths on Balsa stock. Use the marker to draw straight lines.
Cut the base pieces of your structure and glue them together. Make clean cuts, mitering them when necessary for extra hold. Hold the glued pieces together tightly for a few minutes or until dry.
Measure and cut the next lowest set of pieces and glue them into place. Continue building from the base up until you reach the top of the structure.
Leave the structure to dry overnight. Some designs may collapse under their own weight overnight, so be prepared. If this happens, return to step one and try again. You may need to try several designs before you find one that is successful.