Lots of youtube vids on how to glue together a custom tank. It isn't too hard if you're semi-handy and have a good, clean place to work. Basically you need strips of duct tape and a caulking gun with your fish-safe silicone. Have a plan, and have everything laid out before you start, because the glue only has about a 5-10 minute working time before it skins over. Having an extra pair of hands is tremendously helpful, too, so get a helper.
Put several strips of tape on the underside of the bottom with a few inches sticking out; put other strips on the outside of the end pieces. Apply glue around rim of the bottom and up the edges of your end pieces. Stick your long sides on, fold up the strips of tape to hold them in place, and have your assistant hold them there while you place the end pieces and fold over their strips of tape to hold them in place. Run a bead of glue around the inside of all seams for a bit of extra insurance; run a gloved finger or popsicle stick over all the seams to be sure they make a good seal. Boom, done. Let it cure until the best-nosed person in your house can't smell any hint of vinegar in or around the tank--at least two or three days; a week is safer--and you're good to go.
That's one way to do it. Search "how to build a custom aquarium" on youtube and you'll find all kinds of tutorials. Some people mask their glue lines so they're all straight and perfect. I didn't worry about that because 1. Most of the glue lines are buried under the substrate, so who cares if they're pretty? 2. It's easy enough to trim any really goofy glue blobs with an xacto knife, and 3. I forgot to do it. ha ha
The tank I built last winter is 36x10x10, and it didn't need any framing around the top. Yours is a bit taller, so it might, but I doubt it. Good luck!
