When measuring for shocks

Im getting ready to put some shocks on my bagged tbird and im not sure exactly how to set them up.Obviously i'll need to measure from point A to B where I want the shocks for layed and max lift, but what is unclear to me is whether i'll need to get shocks that fit my exact measurements or should I allow a little slack when layed to prevent them from being bottomed out, or does it even matter?

Somebody's gotta have some input. Whats the right way?

BUMPs in the road are more enjoyable with a good set of shocks on your bagged whip!

I'd leave just a little bit of room to prevent damage to them but I wouldnt say that it would matter a lot.

I usually compress the bag/suspension to where it lays or where you want it to stop and measure there. Then get a shock that fits at that compressed height.

I was taught to try and shoot for a shock length equal to about 60-65% of the total suspension travel. Make sure that your shocks aren't bottomed out at full bump and that they aren't topped out at full droop as this can damage them. Are you leaning towards a particular manufacturer/brand for shocks or are you open? The Bilstiens from RCD are a good choice if you have the money, I've also used Rancho and been pleased with the results. If its a real budget build I've used also used good old Monroes from the auto parts store and had it work out alright. Hope this helps you out some man.

Im open to suggestions for shocks, Ill run anything thats been know to hold up and work well. It's not a budget build but im not rich either so i gotta try to spread the funds around for many more projects on this car.
Thanks for the input guys, it was pretty much what I was figureing.