I have a shed with extremely small windows that I use mostly for
storage, but I do have a small area with a work-bench, etc. I also
have a window-mount air-conditioner that I received from a friend
basically free (on a trade). The unit is probably old, but my friend
said it hadn't been used much. This is not an evaporative cooler, by
the way. It's a regular, 220-Volt air conditioner.

I'm planning on building a stand for it (out of treated lumber) next
to an outside wall of the shed and even putting a little roof over it.
Then I'll route the air through the wall of the shed using a round air
duct(s) -- Maybe use an 8 or 10-inch duct(s), I guess.

I'm a complete novice with A/C and the front bezel is missing from the
air-conditioner, so I'm not sure exactly how it works. I assume that
the top area of the unit intakes air and the bottom outputs air. So,
I'm wondering if I need two separate ducts or if I can simply run
everything through one duct? If I use two separate ducts, does it
matter if the ducts are physically close together inside the shed?
Could I simply set it up to suck air from outside the shed and then
open a window?

The air conditioner is much, much larger than what I actually need.
It's rated at 28000 BTU and the shed is about 300 square feet with
open rafters and very little insulation and 4 small air vents in the
roof. I don't use the shed a lot, maybe 20 or 30 hours a year. So, the
electric bill isn't an issue. In the hot weather, like we're having
now though, the shed gets close to 100 degrees, So, I would like to be
able to cool it and cool it off fast when I do need to do a small
project, etc.

I'm guessing I'll have to go down to the local sheet-metal shop and
have something fabricated, but I'm wondering if I might be able to
simply make something out of canvas and PVC pipe, for instance. The A/
C unit will be behind the shed where it doesn't show, so it doesn't
matter if the setup looks a little bit kludgy.