I just had a new roof & vinyl siding put on my home. The guys doing it got shocked while on the aluminum ladder which was leaning on the gutter. Got any ideas why?

You didn't have it grounded. They should have known how to deal with it. But, funny thing is, aluminum isn't a conductor.

Tickle, you are wrong on so many levels. Aluminum is most certainly a conductor, a very good one at that. Gutters don't get grounded because they aren't supposed to have power reaching them. Now where is that juice coming from? Could be several things all of which are wrong. Maybe your power line feeding the house is shorting but I doubt that. Maybe a nail has pierced a cable on the neutral side/ You should get an electrician to do some tests if you aren't up to it. He can measure the voltage and narrow down the source to maybe one particular circuit in the house.

I think I may have seen aluminum used as a conductor, Not one I like.
About the shocking. With info provided, I suspect
The gutter is live,( Nail pierced conductor, or wiring)

If so, Find tester to show gutter live. Turn breakers off one by one to determine circuit.
Then see if turning light switch off eleminates, if it does, nail went through switch leg.

If gutter not live for test, turn on lights.
Hopefully? You only need to replace switch leg.
If they were using tools or had ladder on wire, I will give different answer.
Any more info?