Doors and Windows - how do you measure a Sliding door?

It may sound silly but I can only find vinyl slidng doors measuring 71 7/16 X 80.25" and 72 x 80.75". My opening measures(if i measured correctly) 71.5 x 79". For about an inch difference can that be shimmed(?) or will the frame need to be rebuilt? Your help is appreciated.

Based on those #'s, your opening is too small for either of those doors.
Youre a 1/16th" too wide and short by 1-1/4'-1-3/4" - and thats for a perfect fit which wouldnt give you any leeway for an install.
Are you sure about your measurements?
What are you measuring - the rough opening or whats there now??

well, I measured the door itself(the track/frame around it that is). Is that incorrect? Ho wdo I get a rough opening. How can you compare the doors measurements in the store to a rough opening? thanks for your help.

Do you have any trim/moldings around the door frame? On the inside or outside of the house.
If you do, that trim is probably covering the rough opening.
Remove the trim and try measuring again.
See how that works out.
I presume when youre at the store, youre measuring their doors the same way as youre measuring your door.
I would think that the sliding door frame has a flange surrounding it as a means to nail it to the opening.

ok i will remove the trim and measure that. For the new doors I am just taking the measurements off off the sign at the store so I assume they are giving me dimensions that match the rough opening, yes?

..Within 3/8 - 1/2" or so all around. Generally.
You may have more room than you think once you remove your trim and see how your exisiting window is installed.
That will give you a better idea on your rough opening and whats at the store.(s).