Have done this a couple times now, always so much fun... actually not fun, but not so terrible either.
Warm days are best and be sure to lay out the headliner for a day or two ahead of time to help relax any folds from storage and setting.
Insert the bows that span from side to side. I'd recommend keeping in same order they came out. Start inserting the hard plastic trim sewn onto the edges in the Center front and rear first and work from the center out. Work back and forth between front and rear, get most of the way towards each of the corners but don't finish off the corners quite yet. Next start on the sides in the middle and work your way forward and back on both sides evenly again. All the corners are tricky but with some **extremely** judicious use of a heat gun or hair dryer, the headliner can be warmed to help with stretching to fit.
Your Windows do not need to come out at all. The headliner fits in a flange all the way around the roof. You can use he old liner to help locate front and read dome light mounts and the sun visors and mirror - be careful cutting openings and go slow, you can always cut a little more impossible to put a "little more" back.
Take your time, hairdryer or heat gun helps, but low setting, warmed is enough don't bake or burn it, totally not necessary to get it hot, just mildly warm is good.
My situation is that I bought a shell with no headliner installed.
I have a stack of bows and a new headliner fabric in a bag that measures like 12" by 12"; I have not removed the headliner from the package yet. I have a hard time matching this work instruction with what I seem to have available:
"Start inserting the hard plastic trim sewn onto the edges" Going to have to check, but I don't recall seeing any hard plastic trim on the fabric that I have.
Will have to sort through the long crossbows and see what wants to fit where. I have like 20 of those things.
Nice to know that the windows do not need to come out, that way if I need to leave this for a while it can be done without having to remove glass. I will take some pics of what I am working with and be back with more focused questions! Thanks.
I strongly suspect that buried in your 12 x 12 bag you'll find there is plastic binding around the perimeter - mine came the same way pretty sure you'll find it in there and all will make sense.
As to the bows, I think they were all about the same, my putting in same order probably less important than me believing if they came from there, they'd go back in there easily. They really just spam side to side, nothing complicated about them at all. I'd not be surprised if they were all the same size.
Just doing the mental preparation at this point. The priority is to get the rest of the wiring done and the FITECH EFI working. But I find if I go asking ahead of time I don't get as many surprises. There is enough hybrid systems in this car, the headliner might make a refreshing change since it is all Volvo!