I measured the tanks (duh!) to work out how long and wide to make the shelves. Then I measured how much room/space I needed above the tanks to enable me to comfortably remove the lids, etc. Because I allowed quite a bit of space between shelves, my stands ended up quite tall. Eventually I used the top shelf for my change water, which gravity fed into the tanks on the middle and bottom shelves (easy peasy). I keep a milk crate in my fish room as a step, for easier access to the top shelves.
I made my tank stands with three shelves. The bottom shelf was from memory around 20cms from the floor, to enable me to carry out water changes fairly easily.
I made mine out of extra think pine, thicker than required, but I was also concerned about the weight of water in my tanks. I also used extra thick coach bolts, partly because of the weight issue, but also because they were the coach bolts I used when I built my horse yards/stables/etc.
The first stand I made was a double one, to take 2 x 2 foot tanks on each shelf. Because I was concerned about the weight, I made it with 3 pairs of legs, ie one pair in the middle, but they kinda interfered with access, and the weight of the stand made it difficult to move it around. The next stands I made were designed to fit only one 2 foot tank on each shelf.
To make the shelves, I turned the pine on its side cos it's much stronger that way. I got a bit fancy as I got more experienced, and counter sunk (I hope that's the right phrase!) the bolts.
It really isn't a difficult task. I didn't bother to paint my stands, but painting would finish them off nicely. Building your own stands means you can custom design them to fit into the available space AND to suit your size tanks, etc.
Have a look at the stands in lfs to see how they're made; you'll be surprised to see how easy it is. Before you buy the timber, draw up plans on paper, measure the lengths a couple of times just to be sure (cos that's the part I always got wrong!), then go to your hardware store for the pine.
I really recommend you give it a go. It gives you a feeling of real satisfaction to be able to custom design and then build your tank stands.