I do it first, before painting the wall, with a sash brush, very carefully at the top. The bottom doesn't matter too much as I yet have to paint the wall, but I usually feather it out over 2-3 inches.
What kind of dried paint? What is under the paint on the ceiling? ....on the metal?
I've been a painting contractor for 32 years. Here's how you do it: you're going to need two coats of paint at least. For the first coat, roll your paint parallel to the ceiling to within a couple of inches of the ceiling, then using an angle cut brush of 2 to 2 1/2 inches in width (spend some money and get a good brush; don't use a piece of crap) paint up to within 1/8 to 1/4 inch of the ceiling. I like moving from right to left and painting from left to right into the paint(always paint into the paint you've brushed on the wall, not away from it). When you come back to do your second coat it will be easier to cut a line right at the ceiling because your brush slips more smoothly over the fresh first coat. The difference in color between the wall and the ceiling will make it easier for your eye to tell your hand where to go with the paint. Unless there is a perfectly sharp corner at the ceiling your line will be either on the wall or on the ceiling. In general, it's better to get it more on the ceiling than on the wall, because otherwise, assuming the ceiling is lighter, the line of your new paint will look more uneven from a distance.
Paint the ceiling first. Work top down.
The Sky
Cut-in should technically be done prior to rolling the walls and ceilings because you want to keep a "wet edge" so when all of the paint dries, it blends together. But if you are using a flat paint, this rule is less strict and you can usually get away with doing the cut-in at any point. If after cutting-in (and allowing the paint to dry) you find that you still see the cut-in lines, (and assuming you are using flat paint). Cut-in a second time. The amount of paint on your brush is less than your roller, and cut-in often requires two coats. You will want to "feather -in" the cut-in line into your wall (or ceiling), i.e., dip your brush in your bucket and using the edge of the brush pushed into the cut-in line, apply your paint and drag it along the edge of your line, as your brush releases the paint, stroke the nearly dry brush into the wall or ceiling that you are trying to blend into, this is "feathering." If you are cutting-in with an enamel paint you will probably have to cut-in (do it twice, waiting between coats to let the first dry well) and before the second coat has dried, re-roll the wall, bringing your roller up into the cut-in line.
Michelangelo painted the ceiling of Sistine
Stand on a ladder
Using a white paint on a roof will reflect much of the suns rays; thereby keeping the structure under roof cooler. Paint on the ceiling will have a minimal effect compared to paint on the roof.
Yes, as long as they are both the same base, you can mix many paints.
The ceiling of the Sistine Chapel in the Vatican, Rome.
yes, you can paint ceiling tiles. We have done it many times. Painting may effect their UL listing however.
no