Calculating metal roofing for a shed or garage takes a few measurements and a straightforward formula. Getting the right amount of material before you order saves time and avoids costly shortages mid-project. This guide covers the basic steps for corrugated metal roofing panels in Sacramento and Northern California.

Step 1: Measure the Roof Area

Start with the length and width of each roof plane. A simple gable roof has two planes. Measure each plane separately, then add them together for total square footage. If the roof has an overhang, include it in your measurements — panels need to cover eaves and extend past the wall framing by a few inches for proper water runoff.

For a 20×30 ft shed with a standard gable roof, each plane might be approximately 12×32 ft including the overhang and slope extension. That gives you around 768 square feet for two planes combined. Your actual roof slope will determine the true length of each panel run.

Step 2: Account for Panel Coverage Width

Corrugated metal roofing panels are typically 36 inches wide, but the usable coverage per panel after overlap is approximately 33 inches. This means you lose about 3 inches on every panel for the side lap. When calculating how many panels fit across the roof width, use 33 inches (2.75 ft) per panel, not 36 inches.

For a 30-foot wide roof run, divide 30 by 2.75 to get approximately 11 panels across. Round up to the next whole number — never round down, since you cannot use a fraction of a panel without cutting. So plan for 12 panels across that run.

Step 3: Choose the Right Panel Length

Metal roofing panels near Sacramento are available in lengths from 6ft to 22ft. If your roof run (from ridge to eave) is 12 ft, a single 12ft panel covers the full run cleanly with no end laps needed. If the run is longer than the maximum panel length available, you will need to plan a horizontal overlap of at least 6 inches where panels meet.

Using a single panel length that covers the full run is generally preferred for water tightness and appearance. Calculate your roof slope length carefully — the slope distance is always longer than the horizontal plan dimension, especially on steep roofs.

Step 4: Add Waste and Extras

Always order 10 to 15 percent more panels than your calculated minimum. Cuts at hips, valleys, end walls, and skylights create waste. Damaged panels in transit or during installation can also reduce your working count. On a simple shed or garage with a basic gable roof, 10 percent extra is usually enough. More complex roofs with multiple angles and penetrations benefit from 15 percent.

Step 5: Plan Trim and Accessories

Metal roofing panels alone do not finish a roof. You will also need ridge caps for the peak, closure strips or foam closures for eaves and ridges, roofing screws with sealing washers, and flashing for walls, edges, and any penetrations. Order all accessories in the same color as your panels for a clean, matched appearance.

For a shed, estimate one 10ft ridge cap per 10 feet of ridge length. Plan flashing for any wall connections. Count screws at approximately 1 screw per square foot of roof area as a starting estimate, then confirm with the recommended fastening pattern for your panel profile.

Order and Delivery Near Sacramento

To confirm current panel availability, lengths, and colors for your project near Sacramento, Roseville, Elk Grove, Rancho Cordova, Folsom, or nearby Northern California cities, call 916-940-5700. Have your roof dimensions, panel length preference, color choice, and quantity estimate ready. Delivery and pickup options depend on order size and your location.