If a tile or shingle roof is not too deteriorated it may be possible to restore and buy a few additional years of service at a much lower cost than engaging in a totally new roof.

It is always wise to be proactive and monitor roofs via annual inspection.  Typically, roof deterioration begins with vents and valleys not being maintained.  Left unchecked the deterioration spreads to the wood under the roof.  When this rot begins it may be too late to restore the roof.  

Musts to avoid include putting chlorine on the roof and using high pressure when cleaning.

We suggest that you conduct your due diligence in checking alternatives and warranties.