The table is triangular to save some space, and to be level and rock solid under any circumstance(just in case your shop floor is wavy).
Step 1: Collect the Parts
3ea Heavy Duty locking swivel casters
3ea 4"x4"x32" square tube, or 4" dia. round tube
6ea 2"x2"x30" angle
Assorted metal plate (I used 1/8" and 1/4")
Step 2: Start Welding the Legs to the Stringers
The 2" from the bottom is there so you will be able to tighten the bolts on the casters later.
Step 3: Finish the Welding of the Legs
1)Stand the table on it's top and clamp the angle to the workbench.
2)Take 2 pieces of angle and make a triangle with the table legs you just finished. Tack weld them in place.
3) Tack weld a table leg to the apex of the triangle you just created.
4) Tack the remaining angles as stringers.
5) Fix your symetry issues, and complete the welds.
6) Grind off the rough welds and spatter.
Step 4: Make the Caster Feet
1) Measure your casters and caster bolt hole placements.
2) Transfer the measurements to the metal plates. Cut to size and drill holes.
3) Weld to the table legs.
Step 5: Complete the Table Top
What I did - welded a plate to the top of the table, and another one to the stringers.
What I should have done, and still might do - Flip the table over a piece of 3/4" plywood and trace the tabletop shape on it. Remove the table and enlarge the shape of the table slightly so there is some overhang (2" to 3" on each edge should do).