Just by means of some background, having a new network site isn't an application process as such - operators choose areas where they require a new site and search for locations that will satisfy numerous requirements.
An interested landlord is always a good start, but an existing structure will need to pass structural and (very likely) planning consents before being deemed suitable for use. There may also be additional power requirements.
Out of interest, what do you mean by existing sites being beyond repair? Radio equipment can be replaced if necessary, or is this a structural issue?
