If you have access to CAD, then you should have little trouble building your own cabinets, as long as you are proficient with some carpentry tools....or have a friend who is. Don't know the height of your wheelchair, or how high you sit in it, but I'd go at the lower end of your projected height, just to make sure you can reach things ok.
For materials, us a 2x4 frame...for a 55 gallon, don't get too concerned about "extra bracing". Just build a simple frame with a center brace under the cabinet top. Then sheath the whole construction with 3/4" (or even 1/2") plywood. The type of plywood depends on how you like the looks. If you will paint it, use anything but OSB....just use "REAL" plywood. I made my complete setup using these guidelines, and my setup is fairly "over-built" by cabinet standards...which is what I like! Check out my link in my signature area of my post....just copy and paste (can't figure out how to get a link place there!....grrrr!)