Our potential builder has said they don't offer polished concrete flooring and if we want it - we'd have to organise after handover - is that a possible option?

Yes it is! As long as your new house is built on a concrete slab it can be polished.

If possible it would be a good idea to ask the builder to advise the concretor that the slab will eventually be polished. You could also pay the builder extra and ask him to specify the concrete slab as 32MPA which will ensure a harder finish.

However even if these things do not happen any concrete slab can be polished. We polish slabs in older homes every week of the year so a completed new house is no problem.