If you’re thinking about re-roofing, or even putting a new roof on a newly-constructed building, you ought to consider metal.

The old corrugated tin roof days are gone, and metal roofing materials have some serious advantages over the more traditional roofing materials like asphalt wood shingles.

For most people, replacing a roof is best left to professionals, and if you have a good metal roofing contractor in your area, you definitely want to enlist their aid first, if only to get an estimate. Sometimes roofing contractors get such deep discounts on the large quantities of roofing materials they buy that they can do the job, for the same amount or less, than you would pay for just the materials. If that’s the case, it just doesn’t make any sense to try to attempt it yourself.

But if you’ve checked with your contractors and are determined to forge ahead, here are twelve steps you’ll want take toward that beautiful new roof.

1. Determine the size of your roof

This part isn’t as simple as it sounds, and requires a very long measuring tape and some math skills. First you’ll need to determine the slope of your roof, which can be calculated as a fractional number—with the rise of the roof as the top fractional number, and the run (or length) of the roof as the bottom number. The bottom number is always calculated at 12 inches, so your slope will be something like 4/12 or 8/12. Steeper roofs will have higher top numbers, and low-rise roofs will have lower numbers. Once you’ve determined the slope, convert the fraction to its equivalent in degrees of pitch, and then to a decimal.

Then use the slope factor to determine the actual area of your roof. You can do this without a ladder, by just measuring the length and width of your house on the ground, and multiplying by the slope decimal. Once you know the square footage, add 10% for waste, and you’ll know the amount of roofing you need.

2. Buy the materials and get your tools ready

I like to set up a workspace on a side of the house that has room to work and easy roof access. Use sawhorses or a portable worktable to make your work easier. You’ll also need a metal-cutting tool like a saber or jig-saw with metal blades, aviation shears or a power shear, and a good portable drill.

3. Check your insurance policy

Get a sturdy, heavy-duty ladder and an assistant. Every year, people fall off their roofs and sustain serious injuries, or die. Make sure that doesn’t happen to you. Don’t work alone, take great care especially on steep roof sections, and make absolutely sure you have a good, sturdy ladder. Never, ever attempt any roof repairs with cheap, wobbly, six-foot ladders—they invite injuries.

4. Get a debris bin delivered

Lots of companies rent large haul-away debris bins, and if you’re tearing off existing shingles you’ll need one. Old shingles are dirty, so wear gloves and a dust mask.

5. Rip off that old roofing (on a clear day)

Plan to do your work on a set of days when the weather report has a high level of confidence that it won’t rain. There is nothing worse than trying to re-roof in the rain. Always begin tearing off your old roof at the peak and work your way down. Nail in temporary slats to stand on if your footing feels shaky. Remove every shingle, as well as all the old metal roof flashing. Pull or pound in exposed nails.

6. Repair wood trusses, beams and plywood

Now that you’re down to the wood structure that underlays your roofing material, you’re likely to find some damaged or rotted wood. Don’t ignore it! Now is the time to repair or replace every beam or piece of plywood that looks bad. Be careful where you step! More than one roofer has fallen through a rotted place.

7. Gutters

If you have gutters, you may want to give them the attention they need now—any leaking areas or problems can best be fixed at this stage. Some roofers remove gutters before they re-roof, but it’s not usually necessary when re-roofing with metal.

8. Staple your felt or insulation into place

Once the wood underlayment of your roof is solid, a careful roofer will seal the seams between adjoining pieces of plywood. A good waterproof caulk or silicone sealer works well at this stage. Then, and only then, get out your stapler and attach the roofing felt or insulation your metal roofing manufacturer recommends. Cover the entire roof.

9. Flash the eaves

Roof flashing—the metal edging that overlaps and protects the wooden substructure of the roof—usually comes in rolls or long strips. Nail it to the entire perimeter of your roof, and seal the edges with caulk or silicone.

10. Start installing the metal panels

Finally, here comes the fun part. Work from the longest peak-to-eave section of the roof first. You’ll want to overhang the vertical edge of the first panel about an inch, and align it so it’s completely straight. Metal roof panels typically attach with screws that have built-in neoprene washers, and you’ll want to space those attaching screws evenly—they’ll look terrible from down below if you don’t measure and space the screws well. After that first panel goes on straight, it’s a simple matter of overlapping panels (I always use a bead of sealant in between panels, although some roofers feel that’s overkill) and screwing them down, trimming with shears when necessary. Don’t overhang your panels too far, or water will shoot off the roof and miss your gutters.

11. Flash your roof

Add flashing over the exposed joints where the panels meet at an angle. Use flashing on peaks and valleys, and cut your flashing metal carefully—the sharp edges make slicing a hand very easy. If bending your flashing metal is necessary, use a long two-by-four as a buck—it will allow you to make a clean, continuous bend.

12. Trim and seal

This last step involves the clean-up work necessary to make your roof look finished and professional. Trim off all ragged edges, and use sealant to plug any errant holes or voids.

Voila! You’ve got a handsome, long-lasting new metal roof, and all the work was worth it.