Having been in a similar situation, were I you I would want to find some way to have insulation and air space. You did not say where the house was located, nor sun exposure. Were it in a colder location and out of the sun you may want to take that into consideration.

: I'm evaluating purchase of a lake home that has an alphalt shingle roof, with 1/2" plywood, felt beneath. Between the plywood and living space is 5" x 1/2" tounge & groove boards.

: The house has central air and heat but will typically be used for 3 summer months of the year. Is it worth restructuring the roof to provide an airspace and insulation? What issues can I expect if this is not addressed?