I didn't want to pipe in for I do this daily (for the private sector). And knew there were some municipality / state workers on here. But advice is free along with freedom of speech and I have no illeagle open contracts. So here it goes... Hate me!
My house was added onto before I bought it. Just a side porch but Durham permits anything above dirt (not required in any other municipality around here). But it's simple proof from the ortho's and sale date from GOMAPS (Durham GIS) that it was the previous owner. I had planned on adding another 4' on the rear before the next fly-over JUST so I could blame it on the prev. owner but I got hammered with work. And Durham slipped in a fly-over at 5 years (last year) when it's average every 8 simply for income to catch this stuff for they are so hurting for money and twiddling thumbs right now. They (like all other municipalities) have 2-3 people that all they do is overlay ortho's. Sometimes they catch it and sometimes they don't for look at how many they look at and you have tree coverage and such and some more obvious than others. Glad I got busy for I could have gotten busted.
But... I'm with technologyteacher. Negotiate but don't go to the municipality unless you want added unneccesary headaches. Permitting these days lasts on average up to 1 full year for the municipalities are so starving. I just finished a simple (internal) bath add that the permitting lasted 7 months and $1,800 in fees from a previous client that didn't take my word in Town of Morrisville jurisdiction. Trust me for I work with ALL the local Municipalities every single day. The red tape is gotten WAY out of hand due to NC is so broke. And when things finally let loose around here, there's going to be so much of a back log due to redf tape that they will have no choice but to loosen up.
The only thing gained by permitting someone else's mess (if you even want to go there?) is to add square footage / baths / bedrooms whatever it is you have in your situation to gain for a higher tax value if you plan on selling it. But in return, will cost you more in taxes every year and headaches.
I suggest to get a private inspection if you're not knowledged on how to fully inspect yourself. I inspected my first house myself 18 years ago for all I've done growing up was residential construction. It was in Wake County. With a fine tooth comb! I negotiated a price of $75,000 + closing initial fees ($1,700 back then) when the asking was $117,000. They were in a situation where they HAD to sell due to divorce and a strange X that malested the lady's girl. And he hung in the neighbor's yard every day watching me. But I done the work before closing myself so it wouldn't depreciate and negotiated all of the material and labor in with the closing cost paid by the owner. My realtor was very amazed with me. Your situation would be to use it for negotiations by taking the added unpermitted square footage and pro-rate.
But take my word and DON'T report it to the municipality if you plan on buying it. If you don't want the house, simply walk away. I've given this advice many times in the past few years with every single one that reported came back to me saying I was right. Hate to be that way but it's all down to money. And it's usually better to ask for forgiveness than to ask for initial permission. As long as you aren't adding on yourself and dodging obvious permits which is "double permit price" if caught there's no mercy down to the end. Each initial inspection fee doubles from the previous anyways. (ex. 1st inspection = $99; 2nd if didn't pass = $198) Read your municipalities UDO thoroughly and you will see exactly where I'm coming from! And compare with older UDO's! Search your municipality web and read the rules and restrictions that are added daily.
Wake county's getting ready to require septic inspections annually. That's an extra $100+ per resident. They are so broke...