Ok you need to cut your legs at an 8 degree angle on the bottom and then cut your length at 27 1/2 inches
Then cut 2 squares. One 15 inches and one at 8 inches
Then mark the center of one side and use a straight edge to 2 corners making a triangle.
Then you come 2 1/2 inches on the small sides make a mark and square cut it. Then on the big tip just measure down to whatever looks ovoid and square cut it. I don't remember but my big point was cut down to. For your big shelf you add one inch on your square cuts.