One feature on the exterior of many homes is the existence of rain gutters and downspouts. This creates a system that allows melting snow and rainwater to be channelled through the gutters and downspouts and to an area away from the building. This protects the foundation of the building by preventing water from collecting near the foundation, which can cause erosion and damage the foundation. You can install a gutter system on your shed in order to accomplish the same purpose.
Hammer a nail halfway into the fascia 3 cm (1 1/4 inches) beneath the flashing on the side of the shed. This nail marks the high end of the gutter. The fascia is the board that covers the rafters underneath the roof.
Hammer a nail halfway into the fascia at the other end of the shed to mark the low point. The gutter should be sloped 1.3 cm (1/2 inch) for every 3 m (10 feet) of length, so if your shed is 3 m (10 feet) long, the second nail should be 1.3 cm (1/2 inch) lower than the first nail.
Snap a chalk line between the two nails.
Locate the nail heads where the fascia is nailed to the rafters. Mark the chalk line at every alternating rafter.
Drill a 1.3 cm (1/2 inch) pilot hole into the fascia at every mark.
Screw fascia brackets into the holes with 6 mm (1/4 inch) stainless steel lag screws. If you're having a hard time screwing the lag screws into the holes, rub some soap on the threads.
Measure and cut the length of the gutter to fit your needs. For a structure this small, you most likely won't need to connect two separate lengths of gutter, but if you do, overlap the two sections by 20 cm (8 inches) and connect them with pop rivets.
Connect the end cap to the end of the gutter by installing pop rivets spaced 2.5 cm (1 inch) apart. Apply a thick bead of silicone caulk to the seam between the end cap and the gutter to prevent leaks.
Lay the gutter upside-down and hold a downspout outlet on the end that will be the low end of the gutter. Trace the outlet onto the gutter.
Drill 6 mm (1/4 inch) pilot hole into the centre of the tracing.
Flip the gutter over and drill a hole for the downspout with a 10 cm (4 inch) hole saw, using the pilot hole as a guide.
Slide the downspout outlet into the hole and attach it with four evenly spaced pop rivets. Apply a thick bead of silicone caulk around the joint.
Slide the gutter onto the brackets that you installed on the fascia. Rotate the gutter upward until the back edge catches the hooks on the back of the brackets.
Drill holes through the front of the gutter where the brackets are located and the screw-mounting holes in the brackets with a 5 mm (3/16 inch) drill bit.
Connect the gutter to the brackets with 2.5 cm (1 inch) long #8-32 stainless-steel machine screws and flanged nuts.
Wrap a length of strip mitre underneath the joints in the gutter and attach it with eight pop rivets.
Attach a downspout elbow to the downspout outlet protruding from the bottom of the gutter. Place another downspout elbow on the ground directly beneath it and measure the distance between the two elbows. Cut a length of downspout to fit between them.
Crimp the edges of the downspout elbows just enough to fit them inside the downspout, using a pair of needle-nose pliers. Slide the elbows inside the downspout and connect them with pop rivets or screws.
Consider placing a rain barrel at the end of the downspout. This not only helps prevent runoff, it can provide you with a supply of water for watering plants and trees in your yard.