Tall stories and building work offer scam warning

I'm near Chestnuts Park, in the St Ann's LTN, in a mid terrace house on a fairly small street.

About an hour ago I answered the door to a man who started talking about building work, but I wasn't sure what he was saying. I told him that I don't buy anything from doorstep sellers (goods or services). He responded oh no, I'm not selling, but we're putting up scaffolding and the end of your street will be blocked for 15 minutes - you won't be able to get in or out if you have a car or you're walking. We don't have a car, but even someone who doesn't know that should realise that at this time there is space available to park outside my own house. And it seems very improbable that scaffolding would prevent me getting out of all four corners of my street at the same time on foot or by car! And for 15 minutes???? I was a bit puzzled but wanted to get back to whatever I'd been doing at the time, so was just about to say ok, thanks and close the door. 

Then, the man who's "not selling", just telling me he's barricading the whole street with scaffolding, said oh, and then told me something intended to be alarming about my roof. And, oh, we can fix it for you for free. 

This man didn't seem very plausible to me, and I'm generally quite distrustful of builders. I know good ones exist but I'm sure they have plenty of work to do without trying to scam middle aged women like me or my neighbours, some a bit older, some a bit younger. But if someone who sounds like this guy turns up on your doorstep, just say NO.