Measure the height you want your table to sit at, leaving an allowance for the thickness of the marble. For a coffee table, the standard height is about 16 inches, while the height for a dining table is about 29 inches.
Measure and mark the height on the 4-by-4-inch pieces of wood. Use the rafter square to mark a square line where you are going to cut.
Cut along the squared lines with a circular saw, creating the legs. You may need to cut from both sides to go completely through the 4-by-4s.
Measure and cut the four 2-by-4s so that they form a base along the edge of the marble slab. This is the base for your legs to bolt into.
Glue the edges of the 2-by-4 base together and secure with wood screws.
Glue the legs into the corners of the base and secure with clamps. Pre-drill holes to fit the 1/4-inch bolts through and slip the bolts in from the outside of the base. Tighten the corresponding nuts.
Sand down all the rough edges and apply your desired finish to the wood. Allow it to fully cure. Do not apply finish to the top of the table base where the marble will go, as it will prevent the adhesive from forming a strong bond.
Apply construction adhesive to the top of the table base where the marble will sit. Carefully place the marble on top of the adhesive, making sure to line up the edges so that no wood shows from underneath. Clamp the marble to the wooden base. Allow the adhesive to cure for at least 24 hours before use.