If the wing is symmetrical, there should be no difference in top or bottom curvature. But in any case, the ailerons should be considered as the completion of the wing chord; that is, they should be even with both the top and bottom of the wing (if the hinges are centered correctly). In general, when getting the alignment, I believe it's better to have a tiny bit of droop to the ailerons (for lift), than to have any up aileron since that position would act as a spoiler.