If you've never made an acrylic tank, I suggest you do something smaller first. Lots of people are excited to build their own tank only to ruin $500 worth of acrylic and/or have the tank burst down the road. It is hard to cut, hard to fit, hard to get the solvent even on the joints. Nothing is easy about making an acrylic tank. Especially the size you are making which is a standard 125 gallon tank which you can get new in glass for under $400.
Acrylic is good for larger tanks (over 240 gallons). But it scratches very easily and is not a good choice for smaller tanks. 240 and under (on a new tank) the first choice should be glass.