I'm assuming you mean making a DIY canister filter, and not DIY modifications of an existing brand name filter? I think DIY canister filters become a chop job very quickly. One thing I always look at with aquarium products is what items become plastic junk, even after a significant time or money investment. While it is possible to do what you want, I think it is impractical. I recommend you just buy a reasonable retail canister or do a sump.
Mass manufactured preformed plastic does the job really well.
Best diy canister is going to be as variable as best brand name canister. First how much room do you have? What kind of skills, I have seen some really pro looking diy canisters made from 5 gallon buckets and holiday trays. If it was me thats the route I would go for a 75. There is no reason has to turn into junk plastic IF you are willing to tweak on it and work out the bugs as I doubt you will get it right the first time 100%. Google diy bucket canister.
I hope you do this but it isnt the kind of job for just anyone. First you have to enjoy it and second it takes dedication to finishing it RIGHT or its a waste of time and money. I will probably end up building a bucket canister simply because I like diy and making things that suit my needs.
Here are links to two diy filters I have been working on. The v2 is in the build stages and the first iteration is chugging away polishing water like no tomorrow.
Just buy one, I went that route in the past. It was not practical cost wise, or quality wise. If you buy one, you don't have to come home from work everyday hoping that your stupid diy filter hasn't started leaking again. Not saying it cant be done, just saying that it could end up being one of the biggest mistakes you make in the hobby.
If you're really set on it, my model that did end up working consisted of a water tight 3 gallon cooler. It has to have a seal around the lid. I drilled through the lid and bottom edge. Installed a mag drive pump in line. It was bulky and messy to clean, but did work.
You're working with a pressurized system that has to be water tight. Save yourself the time, hassle, and potential lost investment/damages and buy a cheap SunSun 404 or 304 or whatever the 500+ GPH model is. Then grab one of the nano 240 GPH power heads and go to town. Plenty of surface agitation and flow available with that combo in a 75g and it will run you right at $100. It sounds like a lot, but 6"+ PVC isn't cheap and modifying 5 gallon buckets or coolers is a hack job at best.
Leave the DIY to sumps and other non-sealed filters. Pressure is a big deal.
This guy was already posted, but this build of his seems like the most fool proof and cost effective route to go for just the canister, adding in the pump will be the most expensive part of any diy filter build. However since the build is modular you can upgrade/downgrade the pump to anything you want, which for me is the most appealing part of a diy filter build. https://www.youtube.com/watch?v=hL271pKi_qY
I ended up getting 2 (210 gph) inline pumps. Going to work up a primary filter on the intake, floss and a synthetic resin. I'm also going to build in a substrate cleaner, attach a hose, open the valve, it will have an additional filtering so as not to send the dirt from the substrate into the filter. I found 2 12 inch long pieces of 2 inch clear PVC to make the primaries and substrate filter with. Just need to find the time