Welcome.
In addition to @phb’s great questions that we need more information on, it would also help if we know where you reside; what is the aspect of the patio (does it face N, S, etc); is the roof insulated; how much sun does it get, or is it shaded; and finally, what part of the day/year (day/night, summer/winter etc) do you most use the patio?
You may also benefit from reading Radiant Strip Heaters, an earlier topic to do with patio warming.
