Automate pumping water off a flat roof
You may be trying to do something that could lead to a major failure by overloading the roof structure with the weight of the standing water if the pump does not operate properly AND violates the Building Code by allowing too much standing water to accumulate on the roof.
There are many circumstances where a pump could fail, but is even more dangerous with an automatically controlled pump.
In addition, the Building Code does not allow more than 2” standing water on a roof before it can self drain through a roof scupper. (See ICC R903.4.1)
Standing water is not a good design idea. If the roofing develops a pinhole leak, the entire roof will drain through that hole. It’s better to change the design of the “flat” roof to a sloping roof.
I’d spend my time and money eliminating the low spot and forget finding an automatic pump.