Get someone to screw a block of wood to the wall below the purlin, and this will support the end. 4x2 by about 300mm long, horizontal or vertical, it wont matter, with 2x m8 expansion bolts 120mm long.
Or leave it, it's been like that since built and is still up, and it's the buyer's obligation to survey and satisfy themselves of the condition
IMHO the roof is a bit of a mess. Looks like something has changed at some time and the end of the purlin has become unsupported. Also possibly concrete tiles replaced original slates. As woody says, I think a brace support under the purlin down on to the wall would be a good move, but will draw attention. Personally, I would just plead ignorance and try and sell. Buyers prerogative to survey or not.
Years ago we nearly bought a house which turned out to have horrendous structural roof issues, picked up in our survey (big dormer bungalow with a "T" extension where the purlin joint loads fed down through a wardrobe centrepost into gnd floor ceiling joists...). It was a repo, and eventually the selling bank accepted an offer that was about 40% of the original asking price. In the end though, we backed out - it would have been a building site for a very long time and significant other didn't want the hassle. If we hadn't surveyed, we would never have known.
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