Property income

I am sorry if I bother you again, tutor. But I have another question regarding property income exercise:

“Property income:
Richard owns an unfurnished freehold retail property that he rents out. The shop, which was ten years old, was acquired on 1 October 2023. He incurred costs of £8,400 to replace the roof, and the premises could not be occupied until the work was completed on 30 November 2023; this was reflected in a reduced purchase price.

The property was let from 1 December 2023, at which point Richard received a lease premium of £12,000 for granting a 30-year lease. Rent is charged at £664 per month, payable in advance, and five rent payments were received between 1 December 2023 and 5 April 2024.”

1.1 Should the cost of roof replacement be capital expenditure?
1.2 And why in the solution the calculation is £8,400 × 3% × 4/12? At first I thought the reason they included the cost of roof replacement may be because property income is based in cash basis. But in the solution they calculated based in 4 months, which is not cash basis.

2. I thought the premium income should be [P – P*2%*(n-1)]/n with n is the years of lease. Why in the solution they took the whole number P – P*2%*(n-1)?

3. Can you please explain why there is a difference in the way of taxation between landlord and tenant on property income of premium: landlord is taxed on P – P*2%*(n-1), and tenant is taxed on [P – P*2%*(n-1)]/n for that tax year.

Thank you in advance!