Back
The back is 14 7/8" wide by 22 1/2" long., There is a 3 3/4" hole for access to the valve for maintenance. The center of the hole is 16 1/2" down from the top and 5 7/8"" in from the right side. The back is made of 1/4" PVC sheet. There is a 6" by 6" cover for the 3 3/4" maintenance hole. It is made out of 1/4" PVC sheet. The back is 1" longer than the front and sides so that it has a lip for you to mount it. There are four pieces of 1/4" PVC sheet 2" by 1 1/2" mounted 1" in from the edge on the top and bottom edges for mounting the unit to the wall. They each have a 3/16" hole in the center of them.

Top
The top is 14 7/8" long by 4" wide. There are two 5/8" diameter holes in it. One is 3/4" from the right edge, there is a splash guard next to this hole. It is 1 1/4" wide by 2" tall. The bent down part is 1" long. This is the vent hole for the device. The second hole is 6" from the right edge there is a 2 1/4" by 2 1/4" piece of 1/2" thick HDPE (high density polyethylene) foam glued to the bottom of this hole. The HDPE foam has a 3/8" hole in the center of it. There is a 1/8" by 1/8" by 2" long piece of PVC sheet glued to the two 4" edges and two more along the front edge for bracing to the wall. I believe the top would be better off being made of 1/4" PVC sheet. The top is made of 1/8" PVC sheet.

Front and Sides
The front and sides are one piece. It has been bent with heat. It is 21 1/2" long . The front is 15 1/8" wide and each side is 4 1/2" wide. It is made of 1/8" PVC sheet. You could construct it with glued 1/4" material instead to avoid having to bend it to shape.

Bottom
The bottom is 14 7/8" long by 4" wide. There are two 5/8" diameter holes side by side 1 1/4" from the left edge and 1" from the front and back edges. There is a 2 1/4" hole 3 3/8" from the left edge in the center of the bottom panel front to back. The 5/8" holes are for the water inlet and overflow pipes and the 2 1/4" hole is for the 1 1/2" surge pipe.

Inside
The valve rod is 18 1/2" long and made of 1/4" nylon rod. On the bottom end the last 1" is threaded with a 1/4-20 die. There is a nylon washer glued on the nylon rod 1 1/4" from the bottom end. It is .050" thick .250" ID and .685" OD. There is another one of these washers under the 1/4" nylon nut on the bottom of the rod. There is a piece of 1/8 PVC sheet 3 /12" wide by 8 3/8" long with a 1/4" hole in the center glued on the rod 1 3/4" from the bottom. There is a piece of 1" thick HDPE foam the same size as this sheet on the rod next. There is a brace that is glued to the front and back. It is 7" wide by 3 3/4" tall with a 1 1/8" flange bent over to make each side, there is a 3/8" hole in the center for the rod to pass through. On the topside of the brace is a 2 1/2" by 2 1/2" piece of 1/2" thick HDPE foam with a 3/8" hole in the center for the rod to pass through. It is glued to the top of the brace The sides of this brace are what gets glued to the front and back. There is a tee shaped float on the rod next. It is 8 1/4" long by 3 5/8" wide across the top. The arms of the tee are 3 3/8" top to bottom by 2 5/8" from the outside to the center bar of the tee. The bottom leg of the tee is 3" wide by 3 7/8" long. The float is made of three pieces of Styrofoam glued together. There are two pieces of 1 1/2" thick Styrofoam sandwiching two pieces of 3/4" thick Styrofoam that are spaced 3/8" apart to make a 3/8" by 3/4" hole down through the center of the float for the rod.. There is a washer made out of 1/8" PVC sheet glued to the rod 3 3/4" from the top. It is 1/8 thick with a .250" ID and 1.175" OD. The float valve is 1.7" OD at the top and 1.4" OD at the bottom. It is made of 1" thick HDPE foam with a 1/4" hole in the center.

Notes:
All left and right references are from the back view.

Everything is glued with aquarium grade Silicone except the flange and the panel that is glued to the inside of the front with PVC glue.

Bill of Materials

US Plastic
24" x 48" x 1/8" PVC sheet White (#45138) $24.22 (#45086) Gray $15.37
24" x 48" x 1/4" PVC sheet White (#45140) $38.87 (#45088) Gray $30.72 Only 24" x 24" is needed
1/4 nylon rod 8' long (#47831) $2.80 Only 18 1/2" is needed

Aquatic Eco-Systems
1/4" nylon nut (TN14) $0.07
1/4" nylon washer (TW14) $0.19 x 2

McMaster
12" x 12" x 1" HDPE foam (#8619K391) $17.66
12" x 12" x 1/2" HDPE foam (#8619K371) $8.66

Plumbing Supply
1 1/2" schedule 40PVC Tee (#401) $0.88
1 1/2" schedule 40 PVC cap (#447) $0.49
1 1/2" schedule 40 PVC elbow (#406) $0.56
1/12" x 1/4" schedule 40 PVC slip x FNPT bushing (#438) $0.84

That Pet Place
Caulking gun size of aquarium safe Silicone Sealant (#PF0213) $6.49

Notes:
Both US Plastic and Aquatic Eco-Systems sell PVC schedule 40 fittings for a bit more but if you are ordering from them anyway you might be better off combining the shipping. You should also be able to find them locally. Also US Plastic sells 1/4" nylon nuts(#91235) for$8.58 and 1/4" nylon washers (#91236) for $3.40 for 100 of each of them. They also sell a 280 degree F heat tape for bending Acrylic that should work to bent the PVC sheet which forms at 245 degrees F. The tape warms up slowly so the PVC should start to from before it is completely up to temperature.You will also need a stick of 1/2" CPVC pipe and 1 1/2" schedule 40 PVC pipe and the Styrofoam. You should be able to find all of these locally.