do i need special paint or primer
A good quality latex paint will work fine. If the patio ceiling was factory painted, then you will need to clean really well, then you need to sand the surface to help create a bond to the original finish. Clean that well and prime and paint according to the paint manufactures suggestions depending upon the brand you choose.
You may want to spray this ceiling also. You can rent a machine for a few dollars that will help make the finish really smooth. It is also much faster to apply if there are lots of groves or gaps in the panels. However spraying does take a bit more work in getting the area protected from over spray.
When you paint older aluminum surfaces, make sure they are not "chalky", by running your finger across the surface. If it chalks, you definitely need to clean and prep the surface well. Good quality latex paint will bond, but only if the surface is prepared well. I would lightly sand it, then use a cleaner such as trisodium phosphate (TSP) to clean it, following with a rinse.
HOW TO PAINT A VARNISHED OUTSIDE DOOR (NOT IN WEATHER WHICH ALSO HAS A STORM DOOR, WITH GREEN PAINT, DO I NEED TO SAND IT DOWN FIRST? . SCRANTON, PA.
Do not use exterior duration paint which was all the paint store had in satin, which the customer wanted! It took a week to cure, bugs were stuck all over carport ceiling. Sherwin Williams has a fairly new product called (snapdry) it says u can close a exterior door to weather striping in 1 hour. Anyway I love this paint! Looks like factory finish, less worry of overspray on vehicles or what not. Brush & roller you have to work a little fast. What ever your painting upon has to be very clean.