Building query...

[Wazzzer]

I bet you got a white fascia and a 1" gap away from the brick. Air/smoke will go up and in!

You assume correctly lol... It was all wooden fascia before

[tweed]

I bet you got a white fascia and a 1" gap away from the brick. Air/smoke will go up and in!

You assume correctly lol... It was all wooden fascia before

Easy fix then mate. You need to seal that gap  just that wall though

[Ant1981]

I bet you got a white fascia and a 1" gap away from the brick. Air/smoke will go up and in!

You assume correctly lol... It was all wooden fascia before

Easy fix then mate. You need to seal that gap  just that wall though

But isn't that to provide ventilation to the roof? If sealed, he might end up with a condensation/damp issue.

[tweed]

I bet you got a white fascia and a 1" gap away from the brick. Air/smoke will go up and in!

You assume correctly lol... It was all wooden fascia before

Easy fix then mate. You need to seal that gap  just that wall though

But isn't that to provide ventilation to the roof? If sealed, he might end up with a condensation/damp issue.

Still got another two walls for that. Oh and a house 

[Ant1981]

I bet you got a white fascia and a 1" gap away from the brick. Air/smoke will go up and in!

You assume correctly lol... It was all wooden fascia before

Easy fix then mate. You need to seal that gap  just that wall though

But isn't that to provide ventilation to the roof? If sealed, he might end up with a condensation/damp issue.

Still got another two walls for that. Oh and a house 

The house part doesn't make sense as that's not what it's for.

Are you sure the other two walls can provide enough ventilation to prevent damp?

With due respect, perhaps OP could draw a layout before taking advice to do what you suggested.

[Len]

It depends which way the roof joists go.
Those vents are designed to provide ventilation of the roof space, closing them WILL cause problems!

You can do as tweed says but when you get dry rot and woodworm then maybe you will wish you hadnt taken his advice!

Make them take down the structure!
Write a simple, polite letter first and no need to mention the smoking just say that it is compromising the structural integrity of your property and should not be attached.
Then if they dont respond go to a Solicitor, but write to them again first advising them that they will be liable for his costs.