Dealing with ambiguous lease covenants that require tenants to complete repairs or alterations can be subject to the doctrine of Contra Proferentum.
That is, vague terms will be construed by the courts against the party that made them.
This can be a valuable point of law when dealing with what appear to be unclear terms within a lease and will typically appear where tenants are not property wise and have entered into lease contracts which are dictated by professional property landlords. These situations affect small and medium sized private business who has in advertently taken on obligations at lease commencement that are overly onerous or difficult to remove from their obligations.
Seek professional advice from a Building Surveyor before you agree to a new lease.