Auto body repair & detailing: Roof Replacement, ferrous and non ferrous metals, non ferrous metals

Question
I have a 1988 Mazda hatchback with a manual sunroof that I want to remove.  I know of several ways of patching the hole with steel or fiberglass, but how about just cutting it off at the [6] pillars and welding on a non-sunroof version?  That version has a support beam going across it where my sunroof is, which seems a goof thing to have. Plus it would save the effort of removing donor roof liner, removing my roof liner, installing donor roof liner. Is this much more difficult than patching and dealing with the roof liner?  How about reskinning, either with a sunroofless roof skin or, ideally, with aluminum, ala the Mitsu EVO MR? (Would you need a roof picture to answer this?)

Answer
Jim- you are treading only where professionals should go. First, The headliner must be removed no matter what. You can't possibly remove a roof and weld in another without removing the flammable parts- like a headliner, weather seals, and interior trim panels. There is flammable foam and insulation lurking about inside of interior pieces, and sometimes inside of the cavities of the a, b, and c pillars to prevent wind rush inside the panels. If you remove the roof, it must be correctly grafted in- this requires special grafting techniques. You can't butt weld in a roof, windshield pillars, or any other major supporting panel. The strength of the car will be greatly compromised, especially on a unibody car. Then there is the issue of getting the doors to seal up and align with the roof. Using aluminum sheet over the hole will cause electrolysis between the steel roof and aluminum patch- you can't mix ferrous and non-ferrous metals. They will rot each other out in an alarming amount of time. Your only options are to weld or glue in a steel patch, or remove the roof skin from the car's skeletal structure. This will require removing the front and rear windscreens- the front windscreen may likely break in the process. If you have it professionally removed, the glass company won't guarantee they won't break it  removing it- meaning you will have to pay for a new glass if it does break. Same for the rear. Removing a used roof skin is a huge hassle, requiring you to drill out around 80 spot welds, then getting it to release from the cross supports. Many are glued to them. Then the process must be repeated on the roof of the car. The easiest route is a steel patch, with some sort of support underneath of it. This will require  a huge body filler spot- not the sort of thing a beginner will ever be able to make look good. My advice? Learn to love the sunroof, or replace it with an updated model.