Baton size depends upon the configuration of the shell and how much head and side room you require. Ask your shell builder
for common sizes used with their fit outs.
For example, sub floor batons will depend on the depth of the base plate bearers, the size and type of ballast used and how much air gap you leave above the ballast. This needs measuring in conjunction with available headroom following the insulation and lining out of the ceiling. That in turn needs to take into account the depth of any light fittings you are using and the style and design of the ceiling panels themselves.