The axle is part of the wheel, not the frame - maybe you mean what sort of dropout spacing should the frame have? If so, modern track frames have 100mm front spacing and 120mm rear. This matches the axle lengths on most 'real' track hubs (eg DA, Campy Pista, Suzue ProMax, Suntour etc).
There is now also a good selection of hubs with wider spacings (eg 130mm, 135mm) which can be used on non-track specific frames (eg road bikes, mtbs) - these hubs are generally designed to be used on the road and so often come with better seals than track-specific hubs.
If you're having a frame custom made speak to your builder - (s)he should be able to advise you about all this. Who are you thinking of using?