A survey of a flat has to deal with two buildings: the demise you are buying and the block it sits in. Most of the money in a flat purchase sits in the second, through the service charge and the major works bill, and a survey that only looks inside the front door has missed the expensive half.
Inside the demise
Condition of finishes, windows where they are demised, heating, evidence of damp or leaks from above, and any alteration a previous owner made without consent. Alterations without landlord's consent are a lease problem as well as a building one.
The block
Roof, external walls, common parts, and any sign of a major works programme coming. The surveyor can only inspect what they can reach, so ask them to comment on what they saw from outside and in the common areas.
The lease and the service charge
What the landlord must repair, what you must repair, how the service charge is apportioned and whether there is a reserve fund. Your conveyancer reads the lease; the surveyor should be told what it says so their advice matches your obligations.
Cladding and external wall questions
For blocks where this applies, the paperwork the lender needs is separate from the survey and is provided by the building owner. A surveyor can tell you what is likely to be required; they cannot produce it.
Questions people ask about flat survey
Is a survey worth it on a leasehold flat?
Usually yes, and it should be read alongside the lease and the service charge accounts. The three together answer the question the survey alone cannot.
Can a surveyor inspect the roof of a block?
Only where access is available and safe. Most flat surveys comment on the roof from ground level or from common areas and say so plainly.
What if the block has known major works planned?
The service charge consultation papers will show it. Ask the seller's solicitor for them, because a known major works bill is a price negotiation rather than a surprise.