Bigjarv,
you seem to be set on a complex type SEP,
if you are hour building I'm sure you realise that it doesn't matter what SEP the hours are completed on, a simple SEP will suffice and keep the cost down, most airline captains probably will not care or indeed be able to tell the diffference between a PA28-140 and a PA28R-201! However of it is what you want so be it!!
In my view buying a share for hour building is a good move - it worked for me, I was in a group of 16 and availability always very good - you will be surprised how many people own a share and never fly or only fly an hour a month! An internet booking system and clear booking rules maximise availability.
Also with regards to disposing of your share - a larger group and cheaper share worked here, it worked out that with the hours that I required to build - the discount over a flying club rate was greater than the initial cost of the share! So selling the share at the end just made the cost even cheaper.
Although be warned that you have to be prepared to stand a share in unexpected maintenance costs should they arise - it's worth checking that the aircraft has a good and long standing relationship with a good engineer.
Good luck and happy flying
Gaz