wrote

.. The problem is, how do I attach the gutters with this 6 inches of tin
hanging past the wall? (Cutting off the tin is not an option).
blows inside the barn when the door is open (which is usually is
during hot weather, so the animals stay cool).

Call me stupid here, but can you just curl the metal up to make a lip over
the door section without damaging the metal? Just make a sort of funnel
with the existing roof so rain hits to the sides of the door? Like a really
heavy deep socket wrench and work it in parts til you have a 'lip curl' at
least 2 inches deep, might need 3?

If that doesnt work for you, and i'm right in asumptions that look isnt all
that important, 2 other ideas come to mind.

1- using some sort of rivet to attach, take a flange of metal with a 90
degree bend and high enough for your purposes, and just attach this to the
end of the roof as far as you need it to go. Use caulk if the little bits
that get past this is a problem. (It wont be as pretty or easy as just
curling the metal, but it will work better).

2- Using some old tires cut up, and again a rivet gun, put those up along
just like #1 above. The problem is this wont last as well and i suspect in
hot weather they will curl back up too strongly for a longer term fix.