Hell no!!
Save yourself the agony and time and buy one! Everything abou the building process is difficult, not tomention if it breaks or leaks who are you gonna blame it on to the insurance company!
Play it safe and let the professionals help you. Save money on otherr things, you don't want a lot of water on the floor!
The actual process of building an aquarium is fairly straight forward....as long as you follow the correct procedures.
One day, i plan to build a huge tank for my conservatory....8' long x 4' x 4' and it will be made out of waterproofed plyboard sheets except for the front which will be one big acrylic sheet.
Buying is undoubtedly better, but don't just rush out and buy one from a petshop - their prices are notoriously excessive. There may be a source in your area that produces aquarium tanks that are bigger, stronger, and a third of the price. And they'll give advice on how to mount the tank - the glass base can need substantial and evenly-distributed support.
Aquariums are great, and bring a lot of pleasure.