renegotiating offer after building survey

[Notquitefeelingit]

We've had an offer accepted on a house we really like in a location we love. We accepted the house would need some work doing, for example, all the double glazing needs replacing, but thought it all looked sound and happy to live in it and make improvements slowly. Our offer wasn't competitive though, we offered just over the asking price as we needed to find somewhere in a hurry and thought it was worth going for.
We've just had the building survey back and there are some aspects we hadn't accounted for (as I'm sure there normally are). The main ones are:

Potentially unsupported chimney breast.
Potentially inadequate supports to the water tank.
No fireproof glass in internal doors.
Asbestos panels in the garage (surveyor actually recommended garage be demolished as there is also penetrating damp).
Flat roof needs replacing on extension.

Garage obviously sold as an asset but surveyor recommended we not even use for storage, so that's a shame.

There's also a small electricity substation at the back of the garden, which doesn't bother me per se, but I'd like to get an EMF survey done before exchange.

I'd like to reduce our offer to account for some of these costs and take account of the resale value potentially not being as high as people might be put off by the substation but I'm not sure how to do it quickly and respectfully. The buyer is keen to move quickly too, he accepted our offer quickly.

Would you knock 50% of estimated costs (I'm amassing some quotes) off revised offer or go for 100% and expect he will meet us halfway? Would you share the building survey?

following with interest
hopefully someone will be along to offer advice

Also following with interest as think I may be in a similar position. Surveyor has identified asbestos roof on the property I am potentially purchasing too. not seen actual survey yet but surveyor is going to send it in next day or two

Was the house priced to account for a refurb?
Of all the above, I think the garage is the one that would bother me most and doesn't fall into the refurbishment category. I doubt that's been priced in and I'd look for the cost of the rebuild off the house price.
They can of course refuse or pull out so be prepared for that too.

When we bought our survey picked up a bulge in the end wall, we got quotes and gave the seller the option to do the works themselves, or reduce price by cost of works (was 14k), they opted to reduce price

our vendor didn't budge...
They agreed to do some minor works before exchange.

EMF survey fell to us too - but was £225 so for peace of mind worth it. (20m away so not overly convcerned)

I recently had the same issue.

Survery came back with some red issues. I estimated the cost would be 20k. That's how much I asked the vendor to reduce by knowing he would probably wanna go half. And so he did.
If I only went got 10k, he would have only reduced by 5k.

I don't think you can ask for money off for the garage or the flat roof as you could have seen the condition of the garage was poor I assume when you offered? Flat roofs need replacing regularly so again that should have been obvious when you viewed.

You could ask for money for the glass doors, chimney breast and water tank supports though.