Install cap blocks in much the same fashion as the cinderblock base. With the first wall and corner set, start at the opposite corner and set a cap block into position. Fill in the concrete blocks with material that will fill the interior (such as broken pieces of block). Pour concrete into blocks from top to fill remaining spaces.
Lay mortar bed on top of cinder block walls, butter the ends of the cap blocks, then place cap blocks atop mortar bed. Press cap stones into place and check with carpenter's level. Scrap away excess mortar and begin working toward opposite corner. Use trowel to tap the cap blocks even with string line. Repeat the process, buttering the ends before setting into place. To finish, set cap blocks along short wall.
To install the pre-cast stones, place some mortar along the base of the wall along the pad. S-type mortar is a stronger choice for use with stone. Test-fit the pieces, then butter the back of the stone with mortar before setting into place. Install the corners first, then alternate the longer sides as you move up the corners. Along the top, use stones with a flat edge. Mix the pieces for variety, and when the corners start to fill up, fill in the straight pieces between. (Some will have to be cut to size. If this is necessary, use a grinder with a diamond-tipped blade. Alternately, use a masonry hammer to create stones of the correct size.)
Use trowel to add mortar to the joints after every few stones. Work around the small PVC pipe drains with small pieces of stone. At the outside corners, select a large piece of stone with a long-straight edge. Set on wall so an 1-1/2" overhang is created. Turn the corner and set stones right up to overhang. When the mortar dries about halfway, use a brush to smooth out joints and clean away any loose mud.