Being vertically challenged myself (5'7")
I have often times done a truck roof first, then gone back the next day and masked the roof and done the rest of the truck. The key is that you need to have break lines (seams in panels) so that you can tape it off and not be noticeable. Doing it as you indicate depending on the clear you would get some (quite a bit?) overspray which will not melt into the clear. If the overspray concern was just on the edges of where you cleared you could melt it in with blender but it will go everywhere where you have already cleared. Do you have any seams so you could mask it off? If not you'll need to rig up something to stand on (both sides) so that you can spray to the middle of the roof and not lean into it. You could also try taking the wheels off if it is an assembled car but that brings another set of issues with not being able to properly get the underside of the rockers etc.
These are nicer than what I have but should give you an idea of what I'm talking about.
https://www.zoro.com/keysco-tools-van-stand-48l-x-16w-x-18h-yellow-77781/i/G0544457/
When you are doing the roof as part of the whole job start at the edge of one side, paint to the middle, go to the other side and paint from where you left off in the middle to the edge. Doing it that way helps keep you from getting the middle of the roof dry. Plan out how you are going to spray it, practice with the gun leaning out to the middle of the roof, to make sure that you are not going to lean on anything. Remember to drape your hose over your shoulder when you are painting the roof.
