GreetingS again Debbie,
As you have two, 120' runs, the most important thing would be the number of downspouts that are installed.
You certainly do not want the gutter pitch 60' in each direction.
The gutter can be hung level if a downspout is installed every 30'.
I would probably want 3" X 4" downspouts. They are alot harder to clog.
But again, it depends on what is in the contract.
The cost of the larger downspout should run about $10 more in material per drop and the labor is the same. (but the final price is up to the contractor and where he/she buys the materials.)
If you choose to make this change, tell them before they start.
I use Spike and ferrules at every rafter and hangers at about 2'.
If I were you, I think I would try looking on the Alcoa web site and search for gutter installation.
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