Sorry to hear of the issues you have with the landlord.
The extra costs you have incurred are due to the fact the landlord had to carry out works to the external structure of the flat.
They are liable to repair the property - but they should not expect you to bear any additional costs as a consequence of their work. They should agree to pay you for those, or agree to a rent reduction.
I would not recommend you withhold rent as it gives them an excuse to then evict you. Far better would be to consider a small claims case against them if they refuse to pay you for those extra costs you mention. You could do it now or you could want until you leave the property if you are only there for a fixed term.
You could report the landlord to the council's housing department if there are any disrepair issues which are ongoing. The council can step in to help if there are - you can reach them by email here:***@******.***, or telephone 01332 640764.
As for a small claims I can set out how to pursue that if you wish.
The other option is to consider using a lawyer to write to the landlord - this may have more of an effect and it could also help claim compensation for loss of enjoyment due to the disrepair issues.
Here are a few choices for you if you would like to use a lawyer :
1. Knights Law, tel: 01204 655614, email:***@******.***
2. Stephensons Solicitors, tel: 0161(###) ###-####
3. Duncan Lewis, tel: 0333(###) ###-####