I have a pole barn with a steel roof it was cut about 3inches past the fascia will normal sized gutters work?

 

Not too sure - but I am just finishing installing a metal roof on my barn - it has a 4 in 12 pitch with a length run of 27feet on one side and 14 feet on the other side. I have noticed that the water runs down this thing really fast - by the time it hits the edge you have a most amazing waterfall :-) I think 3 inches is way too much and you should ideally be at 1 inch.. is there any way that you can cut it off? Don't use an angle grinder mind you if it has a coated finish - the metal filings will rust and stain the finish. Try to use shears.. harbor freight sell some for 30 bucks but you have to be careful not to scratch the one side that you will be leaving.. I tip my shears in favour to the waste side when cutting.

As for size of gutter.. I have yet to find a 'handy' calculator that tells me the gutter size to use if my roof is made of x type material and is x in size and I live in x type of rainfall area..

If I find one then I will be sure to let you know - but for safe bets I would go with a 6" gutter assuming you have a pretty decent sized roof.