|Thank you for your question.
As this forum relates to income from property and in order to fully answer your query, I may need additional information as you have stated you are the tenant of the property, not the landlord/ property owner.
In general terms, building works which may be deemed as improvements to the existing property such as extensions, dormers, converting a disused barn to a holiday home etc would be classed as capital expenditure, so not claimable/ cannot be used to offset against rental business accounts.
If you were to be the property owner, then if/when the property is then sold in the future, it may be used to offset against any capital gain.
Further guidance can be found here with PIM2025 & PIM2030 as starting points:
Property Income Manual and :
PIM2030 - Deductions: repairs: is it capital? .
I would advise to keep a record of the repairs/upgrades as if they cannot be used against rental income,
it would then be convenient if/when capital gains arise.
Thank you .