The I beams are very easy to use and make a flat, straight, and solid table. I cut the I joists to 15’ 9” to leave a 1.5” Lip on the ends. I cut 9 pcs of 2x4, 21 3/8” long and screwed them evenly spaced and square to the edges of the I beams. I then screwed 3 sets of 2x4 legs, 36” long to each end and the middle. I put a cross piece an inch and a half from the bottom of the legs. Also drilled a pilot hole in each leg and screwed in a lag bolt for level adjustment. I flipped the base upright and set the 2 pieces of 2’3/8” x 8’ MDF board on top. I set them evenly with 1.5” overhang all around. The top matches up with the edge of the legs. The lumberyard cut the board lengthwise for a small fee. I snapped a chalk line down the centerline of the I beams on the top, and screwed the top down. A slight adjustment of the lag bolts set the table perfectly level in all directions. A few extra cross braces and the table is rock solid.
The smooth, flat surface of the MDF board makes a good work surface. I may need to use a piece of thin sheet metal under the weld joints to prevent bubbling the surface of the board.
The whole process only took less than 2 hours by myself, and I could handle the materials fairly easily. Cost was about $100.