Measure your office for the amount of room you will have for your table. Don't forget to measure the door for space to get the table into the office. If you want the table to sit over your file cabinets, then measure the height of the cabinets and add 3 inches for clearance. Get three dimensions -- width, length and height.
Rip the plywood to the width measurement using the table saw. Set the fence and use the feeder stick to safely make the cut. Then cut the plywood to the length measurement for your table. Set aside your tabletop.
Cut another piece of plywood to the same width. Then cut two pieces according to the height measurement, these will be your table legs.
Find the nicer side of your tabletop piece and set that face down. Measure 1 foot from each end of the table then draw a line straight across the table bottom using the T-square at the 1 foot mark. Line up one of your legs on the mark and hold it against the T-square to make sure it's perfectly perpendicular to the bottom. Screw in the L-brackets against the leg and table bottom, three across each side of the leg, evenly spaced across. Repeat for the other leg so each leg has six total brackets holding it in place.
Sand the edges of the plywood smooth. Nail on the molding to the edges of the table top with the finish nails. Remember that the table is upside down so if your molding has a top, you will need to face it down. If you want, you can also put molding on the sides of the legs, or leave them plain.
Stain the wood to the color of your choice (follow the manufacturer's instructions for application and drying time). Apply a second coat if you desire. Wait for the stain to dry completely.
Coat the table, top and bottom with polyurethane. Follow the instructions on the container for application. Once the first coat is completely dry, rub it down with the steel wool. Use 0000 steel wool to rub out any bumps or bubbles in the clear coat. Eventually, you'll see a matte finish. Reapply the polyurethane and allow it to dry. Continue this process as many times as you want. The more times you do it, the deeper the shine and the better the protection on the table.