Roof needs reinforcing ?

[JudgeAndJury]

Hi all,

I'm in the process of buying a property.
The RICS surveyor flagged the roof as being problematic: the purlin towards the front of the house seems to have moved by a few cm and is not fully resting on the diagonal support along its length or on the metal support in the party wall.

- https://imgur.com/a/BV0Tfcl

- https://imgur.com/a/POEmfrj

This (front) slope has been redone relatively recently, apparently with concrete tiles. The back slope is significantly older, and covered with slate tiles.

The purlin towards the back of the house also has issues - it was propped up in a "less than professional manner" with some wooden supports leaning against the (disused) chimney stack.

- https://imgur.com/a/Mvpci6q

The surveyor thinks the roof halves now have different weights which caused the roof to become unbalanced.

A structural engineer drew up a plan involving reinforcing the purlins with diagonal struts every 1/3 of the length of the purlins.

What do you think?

Should I have the vendor fix this, or take it upon myself to fix it after exchanging contracts (and negotiate on the house price)?
Who should I ask for quotes? Roofers? Builders?

 

[blup]

It’s a general carpentry job although a roofer might do it. When I strengthened my purlins it was next to impossible to get someone in that I judged properly skilled and experienced to do such a relatively small job, so I did it myself.

Blup