It depends on the age and condition of your existing roof. If you have a wood shake roof the answer is most definitely yes.  If you have asphalt shingles and they still have half of their life remaining I would say you are fine installing a solar PV system on it.  However, it would not be wise to install a PV system on a roof that has only 5 years or so of life remaining.  In that case, we would suggest a shingle replacement at the same time the Photovoltaic installation was to occur.