clay tiles are lighter than concrete tiles hence the mbao can be spaced more further apart hence savings.
Clay tiles compared to mabati uses more timber since tile spacing trusses are closer than mabati supporting trusses.
Clay tiles have various designs, mainly the flat type or the curved half round or the spanish s type.
As long as the roof is kept at a steep slope e.g 30degrees, no leakage can occur hence no need for mabati underlay.
A common mistake people do is to lay tiles at a less steep degree[22.5 and below] hence leakages hence requiring mabati underlay.
As Iron Sharpens Iron, So one Man Sharpens Another.