Everyone hates pesky rodents! So I have documented two different methods that I have used for catching (and killing) them. The first method (flipping tube) is a cheap and quick fix while the second method (rotating tube) doesn't have to be reset every time.

Step 1: Flipping Tube Method

The first method that I've used involves using an empty toilet paper tube and a rodent's appetite. By luring the rodent towards the end of the tube, the rodent causes an imbalance as it crawls towards the bait. Thus, the toilet paper tube and the rodent will topple off the elevated surface into a bucket where the pest's fate is sealed.

Materials:

Toilet Paper Tube
Bucket Filled w/ Water
Bait (Peanut Butter, Jelly, Etc.)
Tape

Setup:

Choose an elevated surface that is easily accessible to rodents. This should be easy, as rodents can climb just about anything.
Place your bait at one end of your empty toilet paper tube.
Place the tube on the edge of the elevated surface, possibly securing it in place and preventing it from rolling with a small piece of tape.
Place your bucket beside the elevated surface, along the projected drop path.

This method is fairly effective, but the main problem with this method is that it needs to be reset after each use. So, if you think you have more than one rodent, this is probably not the best option. I have had more luck with the second setup that I have listed: The Rolling Tube Method.

Step 2: Rolling Tube Method

The second method, and more effective of the two, is the Rolling Tube Method. In this setup, a ramp is placed to lead up to an elevated surface or the ramp can be placed to lead up to the bucket itself. The bait is placed on the end of the tube away from the ramp, to lure the rodent. As the rodent attempts to walk across the tube towards the bait, the tube's instability and rotation makes the rodent fall into the bucket below. Again, the rodent is on borrowed time at that point.

Materials:

Toilet Paper Roll
Bucket Filled w/ Water
Wire Clothes Hanger
Bait
Material for a Ramp
Wire Cutters
Drill

Setup:

Take your bucket and drill a two small holes on opposites sides near the top of the bucket. The closer to the top the better.
Cut your wire clothes hanger into a single, straight line and bend it slightly at one end.
Thread your wire clothes hanger through one of the small hole that you drilled earlier.
Now thread your toilet paper roll onto the wire clothes hanger.
Thread the other end of the wire clothes hanger into the remaining hole. What you should have at this point is a bucket with a "bridge" going across the top.
Place your bait on one end of your toilet paper tube. I usually try to evenly coat the entire circumference, as the tube will rotate towards the side with the most weight.
Place your ramp leading up to the bucket or the elevated surface. Be sure that the ramp is not too steep.

The end result should be seemingly stable walking surface for the rodent to receive the bait. However, the surface will prove to be very unstable once the rodent walks away from the safety of the ramp to grab the bait.

The great thing about this setup is that it doesn't have to be reset. We have used this one in our barn with a lot of success.