Thread: adapting in-roof central heater to outside unit

Does any one know if this is possible. our outside unit has had it and I have the chance to pick up a cheap in-roof model but not sure if its 1..weather resistant to put outside; 2.. is it capable of heating a slightly bigger house ( Is that BTU's - what is used to measure heat pumping capacity) 3.. could I put it outside with a shelter 4.. am I correct in assuming that an in-roof model may be rated smaller because it is centrally located whereas an outside model is located to one side of house and needs more power to pump to further extremeties. 5.. am I wasting my time due to some plainly obvious reason. Any knowledge accepted gratefully.