Hi Peter Montgomery,
A roof repair is normally regarded as a revenue expense that can be deducted in computing property business profits.
Please refer to PIM2025 for more information on the distinction between 'restoration of an asset' (the cost of which can be deducted from rental income) and significant improvement of an asset beyond its original condition (the cost of which can be regarded as capital expenditure, deductible from a capital gain).
PIM2025 - Deductions: repairs: overview
Thank you.