The points included in our notes on Selling and Buying apply equally to flats and to houses.
The difference, in terms of owning a flat, is that flats (unlike most houses) are subject to a Lease. A Lease is a Deed under which a landlord grants a tenant exclusive use and occupation of the flat for a term of years, typically 99, 125 or 999 years.
The Lease regulates shared use of the building, deals with service charge payments and imposes obligations and restrictions on the landlord and the tenant, for example as to repairing obligations, insurance, prohibited activities, etc.
If the building comprises three or more flats, there is likely to be a Management Company and often this will be owned and controlled by the tenants themselves. This allows all of them to decide collectively how the building will be managed and what repairs and maintenance will be carried out and when.
If there is no Management Company the landlord retains the obligations to repair and insure the building. Provided he complies with certain regulations for example, as to obtaining estimates and consulting with the tenants the landlord alone will determine what works are carried out, by whom and at what cost.
The complexity of Leases tends to make the buying and selling of flats more time consuming and expensive; expertise and experience in this field is essential.