Determine the slope of the eaves on the long porch roof to confirm the natural direction for the gutters to route the water. Use a small line level attached to a string to create a "level" - as long as the length of the main porch - in this case 36 feet. Have a helper stand on a ladder at one end of the porch and hold the string taut as you balance the bubble in the level. The slope is about 4 inches on a length of 36 feet, a significant drop that will facilitate channeling the rainwater into a downspout installed at the far left side of the short porch roof. Another downspout will accommodate the side of the porch.

Use the line level to determine the slope of the eaves on the short roof. The side that intersects the long roof is nearly level, so we snap two chalk lines: one to mark level elevation and one to mark a 1/4-inch drop to the end of the roof. The 1/4-inch drop denotes the mounting line, because all gutters must slope downward at least 1/4- inch for every 10 linear feet in order to drain properly. You will need to consider edge of the porch roof to determine placements of downspouts and types of corner joints.

Take measurements for the straight sections of gutter. The run on the short roof will need an "interior" elbow fitting (90-degree turn) in the corner where it meets the long roof and an "exterior" elbow on its opposite end where it turns and parallels the front of the house. (In this project, we will cap the other exterior corners.) Hold the elbows in place and mark their ends on the eaves at the mounting line.

Subtract a 1/4-inch gap from each end for the seams when we join the straight gutter to the elbows later with a "seamer" strip. In our project, the required length for the straight gutter on this dimension of the roof is 67 inches.

Measure and mark 67 inches on the gutter section, after supporting it temporarily on saw horses. The homeowners have chosen aluminum gutters - these seem to be most popular, although they come in copper, plastic, and wood. The straight pieces usually come in 10-foot sections that you must measure, cut to length, and then join with special connectors.

Prepare to install the downspout on the correct gutter section by first holding the un-mounted length of gutter in place and transferring the downspouts -  position, tracing around it on the bottom of the gutter.

Measure and cut the length for the straight portion of the downspout - our measurement is 75 inches, allowing several inches of overlap on each end to couple with the angled fittings. The two ends on a piece of downspout look the same at first glance, but one end tapers so that it will slip into the end of the next section to make an easier joint. Cut off the larger end with the jigsaw to avoid any damage to the tapered end that will fit inside. Also, be sure to install the downspout with the larger ends of the joints upward and the tapered ends downward to prevent water leakage at the joint.

Connect the remaining straight sections of gutter to each other and the 90-degree corner pieces (interior and exterior) using specially made 2-inch strips of aluminum called "seamers". They overlap the joints and fill in the 1/4-inch gaps we left earlier during measurements.