"In my judgment, therefore, whether costs have been reasonably incurred is not simply a question of process: it is also a question of outcome. That said it must always be borne in mind that where the landlord is faced with a choice between different methods of dealing with a problem in the physical fabric of a building (whether the problem arises out of a design defect or not) there may be many outcomes each of which is reasonable. I agree with Mr Began that the tribunal should not simply impose its own decision. If the landlord has chosen a course of action which leads to a reasonable outcome the costs of pursuing that course of action will have been reasonably incurred, even if there was another cheaper outcome which was also reasonable."