when i was building a canister filter, google search was my best friend. type in "DIY canister filter," and start going through the list. there are lots of different ways you can do this. the most common one i found was the lock & lock container method. how big is the tank you want to build it for? what is the bucket you have? unfortunately, i found planted tank forums don't know too much when it comes to building canisters. i also found that if you are building a canister for more than a small shrimp tank, it ends up costing about the same as name brand filter. the hassle usually involved can be a PITA, making it cost way more in my mind. i may also be building a canister in a few months for my 10g shrimp tank, with left over parts from my first abandoned project. good luck.
10g- future shrimp wonderland/breeder
29g- in progress
A Pimp Named Eheim 350