Ok, I have some crudely scribbled diagrams, though they are a little better than what I usually do believe it or not. First, a front view;
Next, a side view;
Finally, a top view;
This rack will put the top of your top tank at 63", just shy of 5 1/2 feet.
You will need five 8 foot 2x4's. Remember that 2x4's measure out to 1 1/2" x 3 1/2". I prefer using treated lumber for racks, you can get them wet without worrying, it's the same lumber outdoor decks are made of.
You are also going to need sixty 3" galvanized deck screws, you may as well buy a 1 pound box, you will be needing them for the next rack you build.
A circular, table, or other power saw is a good idea, unless you are looking forward to a real upper body workout. A power drill is needed for pilot holes, I set up 2 drills, one for drilling, one for driving screws. A couple of c clamps helps when assembling, another person helping will do just as well. A square is needed to keep things square.
First cut four of the 2x4's to 51 1/2", saving the scraps. These will be your legs. If you want to bring the top of the top tank to 5 1/2 feet, cut them to 54".
Cut one 13" piece & one 28" piece out of each of the scraps, this will give you the pieces for 2 shelfs.
Cut two 13" pieces & two 28" pieces out of the remaining 2x4 for the last shelf.
Asemble the shelfs on a level surface, making sure they are square. The small dots in the really poorly drawn pics represent screws.
Mark the legs at 7 1/2 inches for a 63" height, or 10" for a 66" height. This will be the top of your first shelf. Clamp, or have a helper hold the leg steady while you drill pilot holes & drive screws. Once again, the dots represent screws. Make sure to keep the legs at right angles to the shelf.
Mark the legs at 29" for the shorter rack, or 31 1/2' for the taller rack. Once again, clamp or hold, drill & drive screws.
Follow the same procedure for the top shelf. What I did was leave 1/2" of leg above the top shelf. This will keep the tank from sliding if it is empty, or keep the plywood I put on them from sliding.
Treated 8 foot 2x4's run around $3 each. Box of screws I'm guessing at $5 tops. Lumber prices fluctuate, sometimes they get pretty outrageous during hurricane season. If you already have the power tools, you will get by for under $30, maybe as cheap as $20, depending on lumber prices. I've seen nice untreated 2x4's a few times for under $2, I've seen more that would serve well as an eight foot boomerang.
I got a sheet of 5/8" treated plywood for under the tanks, I can use them as a shelf if I pull a tank. I forget the price on that, I bought a full sheet & used it for other racks.
HTH, any questions, post away!
Tolak