When I was looking at Roomster specs it was very unclear as to what spec breaking system each car configuration came with. Rather than engine size it seemed to be determined by the combination of engine and gearbox type, with DSG's getting discs all round.

I had the Mk1 1.9 TDi with discs front and back (the back ones needed replacing at 20k for some reason!), but the 1.4 TDi which replaced it had drums on the back, tbh I didn't notice any different, mind you I'm not heavy on my brakes anyhow... With a titchy 1.2 TDi I doubt it would ever need the power of discs on the back unless its being rallied, in which case the 1.4TSi might be better!