The Roof Tiles macro contains a Material operator that is probably overriding any material ID changes that you wire to it. The Macro was designed to work with RailClone Colour, so you shouldn't need to randomise the IDs in order to get bitmap randomisation. It could also be the Advanced Randomise Material node. To randomise a different texture per segment, Generate On should be set to 2.
I hope that helps,
Please let me know if you have any further questions.