We have a 28y/o Medical Clinic in a remote area of Haiti. The roof is concrete and has one coat of DryLoc on it which is lifting off in many areas. The roof is 136' X 35' with a very slight pitch to each side. We plan to mount PV Panels on it after resealing. How should I waterproof this roof? The leaks are very minor.
You're probably looking for an elastomeric roof coating.
Primarily, you'll need to clean the roof, repair and fill any cracks/gaps/etc and remove any of the peeling drylok, apply an appropriate primer meeting the manufacturer's suggestions, then apply at least two coats of the roof coating. It would also be recommended that any sloping/drainage issues be addressed as well in order to avoid heavy pooling, where possible.
As usual, cheaper is rarely better when it comes to roof coatings. A white coating tends to last longer and reduce roof temperatures (which should also help with interior temperatures).
My understanding of drylock is once it's applied, you can't re-apply. It's a one-time application. I imagine it's also primarily designed for interior use, so likely wasn't UV-rated.
Jacob has an excellent solution, which is a rubber membrane type roof (typical for flat roofs).
Given your climate/region, however, perhaps you can borrow some ideas from Bermuda:
Finally, the roofs were coated with a mixture of lime, sand and water and, when available, turtle and whale oil to provide extra weather-proofing. Apart from the animal oil, this method of roof construction continues to be used.
Another possible idea may perhaps be to use an epoxy coating of some sort. Certainly consult with an expert regarding that first.