Their are a lot of mistakes an installer can make that you wouldn't find out about until it was to late.
You should hire a Roofing specialty contractor that only hires people with years of local experiencewith the NW winters.
And also gives you a long workmanship warrantee in writing. 
Homes are most peoples #1 asset & the roof needs to do many years of protection from our Great Northwest 
wet fall high winds, winter ice dams, east winds, spring thunderstorms & +100deg. sunny temperatures.

To help costs stay in perspective:
If it was carpet with pad it would cost about $4 per s.f. installed.
Standard slope re-roofs cost about $1.25 per s.f. and it's a riskier location.
Standard slope Tear off adds about    .75 per s.f. per 1st layer & is much more weight removal. 

Hiring co-workers, family or family friends to replace the protection of most peoples most 
valuable asset, your home: 
Your more likely to not insist in the most professional option for the project.
If or when a leak occurs it would be much more comfortable to just call your contractor rather than dealing with the stress & long term uncomfortable relationship at gatherings or at work.
We do this work year round & have in this area & Seattle for 40 years.

When someone needs to get on the roof do it when the temperatures are not extreme.
Best temp:  45 to 65 degree's. and overcast is ideal.

Have your brick chimney inspected and a clear water sealer applied.
Frequency:  every 3-5 years.

Have your metal chimney inspected and a metal sealant applied at the storm collar.
Frequency:  every 3-5 years.

Have your gutters, downspout elbows and drainage checked or cleaned out.
Frequency: Generally Oct. & Dec. depending on number of trees.

Don't  install Antenna's over roofing or chimney's.
Try the attic, gable end or a sat/cable company.

Keep trees trimmed so as to minimize shading on the roof, branches falling on the roof or touching the roof in a storm.

If you have not applied an Algae block shingle, apply a moss killer (only to the roofing )
Frequency:  every 3-5 years after approx. 10 years depending on the shading & dampness.

When prior roof was many layers & ended up extending down further 
causing the last gutter install to be installed a bit low:
Upon multi layer tear off & re-roof, the new roof doesn't extend down as before.
Proper thing to do if visually a problem or gutter functions are in question is
to raise the gutter back up where it belongs. Generally not best to install a large drip edge.
A large drip edge gets very dirty quickly, is not what a home owner/buyer wants to look at
& displays stain marks for the homes entire life.Also gutter screens reduce cleaning allot.

Basketball hoops mounted to the roof. 
Try an independent pole system away from the roof. 
( May be adjustable in height this way also )

To be fair:
All roofing company's once in ten years works for an "innocently confused" customer
very possibly with complaint's posted to the internet. 
Once posted they get spread all over by dozens of rating.com's,
most of which don't offer the company a response option before posting
or notify the company of the complaint.
So only judge negatively if you see complaints from several user names, over time. 

A roof warrantee is not a house maintenance contract or a house exterior warrantee. 
Ask for those if you need that assistance.
You, or your hired company, still need to do ongoing maintenance to all outside items.
Non contracted items are not included in a new roof warrantee. 

Many existing & aged adjacent items can look OK but may be near the end of there economic life.
If an existing, aged adjacent item needs to be manipulated to complete your roof  & if a problem rises,
there is a courtesy check & fix attempt, but no warrantee extended to your pre-existing & aged item.

Roofing tear offs & re-roofs are heavy weight products. One in 200 driveways suffer some minor damage.
If you suspect that your driveway or sidewalk may be weak please let us know as early as possible.

Wind damage ( over 54 MPH for Oregon ) to your property technically becomes the responsibility of the home owners insurance company. Possibly good to know if you have fences, expensive trees or bushes etc. We install our roofs to handle much more wind then 54 MPH but damage can initiate from another location in a wind storm and its to hard to keep track of this. This is why your Insurance Company takes care of your property damage and theirs takes care of theirs.

Ice damage is also covered by most Insurance companies.
Don't even think of getting on even a slightly damp wood roof or even slightly sloped smooth surfaced damp roof!

It is unwise too pay to much, 

but it's also unwise to pay too little. 
When you pay too much you lose a little money, that is all. 
When you pay too little, you sometimes lose everything,
because the thing you bought was incapable of doing the thing it was bought to do.
The common law of business balance prohibits
paying a little and getting a lot – it can't be done.
If you deal with the lowest bidder, it is well to add something for the risk you run.
And if you do that, you will have enough to pay for something better.

John Ruskin ( 1819-1900 )