Roofing tiles should be checked regularly for breaks and cracks or even miss alignment, also checking that roofing felt is present and correctly installed. Flashings at roof and chimney abutments must be checked. If your roof is sound then you shouldn't need a roof tile sealant. Flat roofing can be a problem as this is generally used as a place to install solar water systems, satellite dishes and quite often general junk. Very often the roof has been drilled to fix these items causing punctures in the roof felt or any roof sealant.