The set about designing this stand because I wanted to have my sump in another room. I did not want the sump to just sit on the floor so I set about designing a stand. I wanted the stand to be large enough to hold the sump (30 gal tank) and a small refugium (currently a 10 gal tank) and also provide space to mount the circulation pump. The final dimensions of the stand I built is 7' long X 2' high X 2' wide. To give you an idea how big this is a standard 180 Gal tank measures 6' long X 2' high X 2' long so this stand is one foot longer than a 180 gal tank. WOW!!
Anyway. On to the goodies. Below is a picture of the completed stand sitting outside where I built is. The plywood section that is behind it is 4' X 6'.
I put a bottom shelf on this stand for storage and also raised the stand 3" off the floor so if water should spill it wont be sitting in the water and I will provide a sort of toe kick.

The next photo shows the stand with the doors open.

All in all I used up 7 10' 2X4's and 2 1/3 sheets of plywood building this stand. Obviously if you build yours smaller the amount of wood will be less. All in all I think I have about $100 worth of wood and screws and other hardware into this think.
Cut list:
6 24" long 2X4 sections
4 7' long 2X4 sections
4 24" long 2X4 sections
2 24" X 24" squares of plywood
4 24" X 7' long section of plywood
10 21" (approx) sections of 2X4
Ok that should be the bulk of the cuts that we will need to make. The 10 shorter sections of wood will be for cross supports for both the top and bottom shelf. I say approx 21" because its best to measure them to fit snuggly. This is where your going to get the bulk of your support especially if what your putting on the stand is going to be less than 24" wide. If you skimp on cross supports then you better get thicker plywood. I used 3/8" plywood and I would not put anything of substantial weight on this thin plywood unless you have cross supports.
I used 2 1/2" galvanized nails on all areas that I was screwing together 2X4's. I used 1 2" galvanized screws to secure the plywood to the structure. I prefer screws as they have less a tendency to back out on you. For easier job screwing I suggest pre-drilling pilot holes in at least 1 of the 2X4's that your joining together.
Instructions on how to put it all together