I know someone who's built a shed on their property, and honestly it
looks pretty good. HOwever, I have no idea whether or not it meets
"code." He seems to know what he's doing though. Anyway, it's a
somewhat large shed meant for doing "workshop" stuff, cutting wood,
building things, etc.

Let's say this person has no idea what the "building codes" are for his
area. Thus, it's possible someone could come by and say "tear 'er
down." It looks nice, though, with shingles and painting that matches
the house, and even windows, so it's doubtful any neighbors would
complain.

Ok, so now it's time to sell the property. How does the fact that this
rather large shed has been built (not according to code, although not
necessarily not according to code...fact is I doubt he knows what the
"code" is) affect the transaction, or how COULD it affect the
transaction and life after the transaction?