Fixing Roof 74 Gran Torino

doonor roof off a rust free car is your best bet

I parted out my 73 formal roof case the roof was unsalavagable and needed replacing and a good donor roof was too far away and shipping is costly on thos big items so the cat got parted it had other rust issues like trunk and quarters as well and just not worth the time and money to fix.
You can use a roof off a 72-76 formal roofbut if your car has opera windows in the quarter sails then you will have to find a 74-76 donor roof with sail panels or replace the upper roof to the quarte/roof seam and a 72-76 will work for that.
if the lower of the window sills are rotted bad then I suggest the entire roof with the A pillars cut at the firewall and the whole roof section including the sail panels and rear window and body panel between the window and trunk be sectioned from a good donor car which in Cali would be easier to find good rust free roof sections

hard to say, I have never done a complete roof replacement with sail panels,pillars and all.Done chop jobs.customizing cars and lowering the roof on some old classic hotrods but never paid attention to how long it took. It can be very labor intensive so if your paying a shop to do it it's not gonna be cheap as if you DIY(Do It Yourself)
most DIY hobbyist/restorers wont tackle that big of job unless they have welding and fabrication experience.

on a job like that,if I were to do it fro customet it would be time and materials and not quote a set fee as you never know what you might run into and don't bid jobs like that with a set price cause it will bite you everytime if you do and most bodyshops or resto shops charge anywhere from $45-60 per hour.

just a guess and don't quote me on it would be 40-60 hrs could be more or less depending on the experince of the technician performing the work. At the lowest per hr and time 40 hrs at $45 per hr equals $1800, which for that you can buy a complete bodyshell to swap on to the frame and use your interior and front end and bolt on sheetmetal,rather then cutting and welding on a donor roof and why most people who do it DIY cause the labor cost is not worth it if you have to pay unless you have a friend who will do it cheap