According to tr :
I am adding a 125 amp subpanel to the far side of my house. I need to
add a disconnect breaker near the new subpanel...but...I can not find
anything rated at 125 amps at either Home Deport or Lowes. The
largest they have for disconnect is 70 amps for a spa setup.?

Does the subpanel you're installing not already have a "main"
breaker in it? The disconnect doesn't have to be separate.

Use an ordinary house main panel "package", not a main-breaker-less
subpanel for the subpanel.

Further, in the CEC, you can use a main panel breaker pair
as a disconnect for the subpanel - you don't have to have
the disconnect at the sub. This may be true in the NEC also.

[I _prefer_ to be able to kill the subpanel from the main
without killing the main. But, if there's a long distance
between the two, having a second breaker in the sub
is convenient.]

[Mine has breakers at both ends. A Siemans main panel "package"
with 100A main in the garage, and a Sylvania Commander 100A feeding
it from the main.]

Large breakers (eg: 60A) are certainly available, but usually
not at places like HD except as part of a "panel pack". Large
breakers for old panels are getting _very_ expensive. Just
paid $80 for a 30A Commander dual. Ick. Fortunately the 100A
feed breaker was given to me free from a friend.

Also...I am running a feeder line from the main panel to this
subpanel...the run is about 100 ft...can someone tell me what the code
is regarding the size of wire needed for this run. The retired
electrician at Home Depot says a 4awg three connector cable will be
fine...it is being run through 1" EMT across a flat roof with rain
tight compression connectors ?

4ga sounds right, but you'll actually need a total of four
conductors. Ground and neutral have to be separate in the subpanel
(remove the bonding jumpers).
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.