Okay, different states have different laws, but you need to see about the ones that govern YOU. I have beeen told previously by two separate relaible sources that if an unpermitted building or addition is not caught before the property changes hands the first time, that city-enforced correction is not possible. However, if you ever want to make a future change to the house, you may well have to bring it up to code, which will mean an inspection to determine whether it meets code or not.
Your city's planning department should be able to tell you whether a permit is needed for a small shed, and under what circumstances. Typically one like you describe does not need a permit unless you plan to add electricity or plumbing. You need to deal with someone else, and probably over the phone without giving your real name or address. I think it was already suggested that you act as if you are seeking information for a potential project rather than asking about needing a permit for a previously unpermitted building. One question to ask is the conditions that trigger the need for a permit--that you want to keep the size under that threshhold, or something similar.
Your city's planning department should be able to tell you whether a permit is needed for a small shed, and under what circumstances. Typically one like you describe does not need a permit unless you plan to add electricity or plumbing. You need to deal with someone else, and probably over the phone without giving your real name or address. I think it was already suggested that you act as if you are seeking information for a potential project rather than asking about needing a permit for a previously unpermitted building. One question to ask is the conditions that trigger the need for a permit--that you want to keep the size under that threshhold, or something similar.