I would recommend Henry’s white elastomeric (rubberized) roof coating. You can buy it by the 5 gallon bucket at home depot for ~$100 bucks.
Apply it with a standard paint roller on an expand-able pole (like what you would use to paint any interior ceiling).
The color (silver or white) is for reflectance. Black colored roofs don’t reflect any sunlight and get extrordinarily hot in the summer. That hotness superheats your attics/roof carwl spaces and translates down to the top floor in the house. Around here, it is a common reason why the top floor of your house is so hot.
Silvercoating has been the “typical” color the past 10 years, but is nearly as worthless as black. The color silver only refleects marginally more of the suns rays as does black. This white coating reflects 90% of the suns rays and leaves your roof warm to the touch in the middle of a summer day. You would get 3rd degree burns if you left your hand on your black roof any normal dc day.
The rubberized coating seals your roof. I believe this Henry’s stuff has a 10 year warranty but there are other makes as well.
Don’t bother hiring someone to do it. Most normal sized roofs can be done in a couple of hours so there is no reason not to bread and do it yourself.