The division of costs are simply explained above but look carefully at how the aircraft is managed and what funds are accrued for engine rebuilds and any expensive unscheduled maintenance etc. In the short period that you will be an owner you could be sharing a very large bill. The critical issue for you is the spread of the shareholders demands with regard to the normal days they fly. In many groups it is common for the aircraft to be heavily booked at weekends only and if your preferred days are midweek that should suit you well to hour build.
It is important to clarify with the future group how you wish to use the aeroplane and the hours you expect to fly over a given period. If sufficient held reserve funds are not in place then cash flow may be of concern to some and this can be aggravated when one member is flying intensely.