Catching snakes is not an easy task as snakes are elusive, often aggressive and live in hard-to-reach spots. That's why snake traps are used by exterminators, for a price. But homemade snake traps can be easily and cheaply constructed and can usually get the job done just as well.
To catch a snake at its den, wooden boxes can do the trick. First, locate an entrance to the den, like a hole in the ground or a hole in the side of the house or garage. This will probably be the hardest part. Then the wooden box should be set on top of it, with a valve apparatus sticking into the hole. The valve should be 1 to 2 inches in diameter and the box should have no other entrances or exits that the snake can crawl through. The valve opening should be covered with a hinged piece of plexiglass that allows a one-way entrance into the box. So the snake must enter the box to leave its den and won't be able to get out.
A wire cage can easily be converted into a funnel door snake trap. At one end of the wire cage, the wire should be modified and converted into a funnel that is very narrow so that a snake can just barely fit through it. Inside the cage should be a live mouse or some other bait--live small animals work better then dead bait or just food. The snake will smell the bait and crawl through the small hole in the funnel to eat the mouse or bait. But because the hole is elevated and quite small, the snake won't be able to find its way out of the hole and will become stuck, at least until it has finished digesting the mouse it has just swallowed.
Snake glue traps have been said to be the most effective for catching snakes. A cardboard box can be used and a funnel-type hole is made in the cardboard. Inside the box, glue or very strong double-stick adhesive tape is laid down. And then a small cage with a mouse inside of it is placed inside the box to lure the snake inside. Once the snake is inside the box to get the bait, it will slither over the adhesive and become stuck, trapping it. Then you can simply open the box to view and remove the snake, with cooking spray or some other adhesive remover.