The CCPC also recommends obtaining a booklet titled "What You Should Know Before You Hire a Contractor" from your local CCPC district office. Gutters were an item we did not carefully consider. Our contractor casually mentioned them and we declined. Afterward, we discovered why they were needed. Unlike wooden shakes, which soak up night moisture, other materials drip water, sometimes copiously. We later installed lightweight plastic gutters in key areas and now irrigate some bushes with the runoff.
From our research we learned there are other factors that increase re-roofing costs: roof slopes exceeding a rise of 6 inches in 12, upgrading the under-roof, damaged support beams or dry rot (our contractors would replace up to 100 linear feet without additional charge). If the material selected is heavier than your house can support, the reinforcement necessary must be done by a structural engineering contractor, not a roofing contractor.