Rust never sleeps
Has it been outside? Rain and other weather will have found any weak spots, and will have started to lift paint and widen cracks. Has it been inside? Rusting due to condensation will have been going on, even if the boat's been on land, in the most inaccessible parts of the bilge. If the boat's been well cared-for, as mentioned below, these issues are controllable, but they need to be watched. Tankers are generally geared to a commercial life of 25 about years because of rust working it's way through their plating. This hull is about a third through that.... if the plating was as thick as a tanker's to start with. What are you planning to do with this boat? Roberts designs are not generally renknowned for their great performance. (They make their money selling plans for "easy to build" boats.) Since you probably won't be able to outrun it, will the boat hold up in bad weather? That's where the builder takes on importance. How carefully did he follow the plans? There are welders who work on submarines and who build boats in their spare time, and there are welders who fix lawnmowers and who build boats in their spare time. There are guys who learn to weld by building a boat. Who built this one? There are a lot of questions to answer before buying any boat, especially one as big as 36feet. The fact that there are relatively few boats of this design and their construction may or may not be top level should raise warning flags and adds to your homework. If the answers you find leave you reassured, rather than bringing up further questions, have fun sailing. Another boat might be a better bargain, though even if it were more expensive.