Clipped from a site...
Step 1
Ok, first buy the wood. Don't skimp here. The whole look of the stand will depend on the quality of the wood you buy. I went with 3/4" A/C plywood. The A/C are grades of the sides of the plywood with A being good (no knot holes, and C being Ok, a few smalls ones maybe). Of course the "A" side would go on the outside. Also, knowing that the inside of the stand will be humid and that the four courners are the most important part, I got 4x4 treated posts.
Step 2
This is the fun part, the frame. I did this by notching the 4x4 posts so that the 2x4 frame would fit. This way, the upper and lower frame rest directly on the 4x4's. I fastened the 2x4 boards to the 4x4 posts and other 2x4 boards with deck screws. Here is were I added the 2x4 braces I put across the top and down the front and back in the middle too keep the stand from bowing over time. The are pictured in step 4.
Step 3
Fasten the playwood to the frame. I put plywood on all sides except for the back. I then measured and cut the holes for the doors with the whole thing on it's back. This was easier to do this way but a bit riskier as if I made a huge mistake, taking the plywood off would have been a chore. The top piece of plywood is 48 1/2" x 18 1/2" (if I remember right) to match the 90 gallon aquarium bottom. The plywood sides come up a bit over the top of top piece forming a small lip. No pratical reason for this really, it was just how I designed it. I also designed the plywood to extend back past the frame for an inch or two back from the frame so I could put the stand against the wall, but have the frame and the aquarium out a few inches.
Step 4
Here you can see the inside of the stand with the middle braces I added back in step 2. One change I would make if I could do it all over again would be to put the metal brackets securing the back vertical 2x4 on the outside of the frame, instead of the inside. This would allow easier removal of the brace to remove a large sump if necessary (which is was).
Step 5 (Sides)
This is when I added the molding and doors. One note, glue, just don't nail these on. When you get your friends over to move it, they will more than likely pick it up by the molding so securing well is in everyone's best interest.
Step 6 (Front)
Here is a pretty good shot of the front of the stand before staining. And for those computer geeks out there, yes that is an old IBM mainframe in the background. They make excellent tool storage closets!
Step 7
This only thing left to do was seal the inside. I water sealed all the wood inside the stand and calked all the seams. I figure the stand bottom will hold approx. 10 gallons of water if something happens in the sump. I just hope to never test it. I then put two coats of stain and one coat of sealant over that. I looks good, doesn't scratch easy, and repels even saltwater!
Hope this helps???