Use a speed square to mark the bottom of the four legs at a 90 degree angle, so that 3-1/2" is left at the bottom, as shown in the diagram.  Use a circular saw to cut off the back.

Find a level surface to work on.

Drill two pocket holes (1-1/2" material setting) on each of the inner apron boards.

Attach to the legs, so the legs are splayed outward, and the outer top edge (face down on the tabletop) is flush, using the 2-1/2" pocket hole screws.

This step is much easier with a second person helping support the legs. 

Please watch the video first on this step to demonstrate how we attach these pieces easily and accurately.

From scrap wood, cut two blocks, 12" long, to help hold up the seat support frame while you attach.

Attach one of the longer seat frame boards first, with even overhangs on the ends (past the legs).

Then attach the two half supports.

Build the second half of the seat frame using the first half as a pattern (just set the boards on top and screw together).  Then flip into position, support with the temporary blocks, and attach.

Build four bench frames on a flat surface with the screws.

Attach centered on the base of the legs with screws.

Attach cross supports inside the bench frames.

Flip the picnic table over on to a flat level surface.  Attach the small seat supports as shown with glue and screws to the eight smaller bench legs.

Position the seat boards on the frames and screws down.

Build the inner tabletop frame first using pocket holes.

Position the tabletop boards on top of the frame.  Screw from underneath to attach.

Then cut off any excess with a circular saw from underneath.

Attach the finished tabletop to the base with screws from underneath.