Restoring The Roof from a bad SunRoof
Probably the easiest way for someone with access to a welder or a friend with one, some extra bucks and a ready source of a roof, is to replace the whole roof. However, most people fall into the category of I'd rather not invest that much time / money into it.
If you have access to a welder, but do not want to tackle the whole roof replacement for whatever reason, try this method. This is how we repaired an aftermarket roof repair on another vehicle.
You need to get a piece of sheet metal that is big enough (at least 1" wider AND taller) that will readily fit in the opening. The problem with Flat stock, is that it does not have the gentle curves of your roof, and you will spend more time and money trying to blend the patch back to the roof line than if you had replaced the whole roof.
So, Find a donor roof. This way, with careful measurement you can find a piece of sheet metal bent to fit within the hole you currently have DON'T CUT YET. Next step, after removing the old sunroof and cleaning the hole edge completely, even to the point of grinding off the old paint all the way around the edge, even underneath if possible, also pull back the headliner, or since you'll be replacing it, remove it entirely.
Get a Flanging Tool. You can either get the one that attaches to your air hammer or the one that is actuated with the ratchet. With either one you need to be careful NOT to introduce waves of stress into the metal, but the choice is up to you. The Air one is quick, but requires a bit of skill, the ratchet is slower and harder to use, but in the long run provides a smoother and more consistent flange. These are both available from Eastbrook (click the sponsors!)
The flanging tool will provide a LIP for the donor roof piece to fit into. Once you've flanged the whole opening, this should have helped stiffen the hole so you don't have that washboard effect. NOW measure your opening from the flange step to the other flange step for the SIZE of the piece you need. BUT BEFORE YOU CUT THE DONOR ROOF, identify WHICH section of the roof to cut.
To make this simple, extend the "straight" edges of the flanged hole to the "corner" that would be there if the hole weren't rounded, and hence the flanged lip rounded also. By extending both the horizontal and vertical lines you will have drawn 4 corners on your roof. These corners will then be the basis for identifying which part of the donor roof to cut out. By the way, the line you extend should be the indented or lower curve JUST as it meets the bend in the metal. In this manner you are measuring ONLY the metal you need to fill the hole and not the dimension of your flange.
To do this, from the front right MARKED corner of the flanged hole, FROM THE MARK measure to both front pillars. You might make a small mark on the pillars that can easily be transferred to the donor car. Repeat this for the remaining 3 corners. By having a PAIR of measurements, you will be able to ascertain with ease and exactness the exact location of the 4 corners. Now transfer all 4 pairs of measurements with the same care to the donor roof. (Usually if you buy the whole roof from the bone yard they'll include short sections of the pillars)
Now by connecting each of the marks with STRAIGHT lines, you'll have your cut lines on the donor roof. Don't worry about rounding your corners yet. Once you're sure of location and everything else, cut the metal from the donor roof. By the way, Metal Shears WILL deform the edge of the metal, don't use them here, same with tin snips, and even both electric and air "shears". I recommend a Jig Saw with a new metal blade operating SLOWLY. Trust me you do NOT want to introduce bends in the donor metal. While you are working, have someone support the roof from inside to minimize vibration and also the piece from flapping in the breeze.
Place the donor metal on your car, make marks on all the edges to advise whether you need to grind to get the new metal within the flanged area giving you about 1/16" of an inch (no more is really necessary) all the way around. Work FIRST with the straight edges then go to the corners. Fit these in the same manner.
If you've taken your time, you will at this point see the beauty of doing it this way, the donor metal should show that very little blending in should be required after you finish the welding and bondo or lead.
Last item, when you go to weld or braze, use a heat sink compound all around the perimeter of the opening, and tack the new piece in place with small tack welds or braze spots around the perimeter. DO NOT OVER HEAT THE METAL. This is the main reason people end up having to work their roof for hours.
If you want you can first rivet the piece in place so it will not move during the welding, but rather than a rivet I prefer the panel clamps available from Eastbrook. These fit into a rivet hole and clamp the two pieces of sheet metal together strong enough to allow for a weld. You only need 2 or 3 well placed holes to hold the whole panel, don't get crazy, every hole needs to be closed afterwards.
Work carefully and quickly around the edge, keeping in mind that too much heat equals a warped panel equals an hour or two of MORE body work PER WARP.
Once you've gone around the whole perimeter, you should have a waterproof weld / braze, a strong patch that actually helps reinforce the roof sheet metal, and most importantly, a surface that will take very little filler to smooth out and blend in.