It's probably best for you to work out what size of opening you require and go from there, just remember that each leaf will not normally exceed the width of most standard domestic doors (about 2ft 6in to 2ft 9in or 762mm to 837mm each in many cases - measure yours) and that if they did they would start to look out of proportion in comparison to other doors in the rooms they connect. In terms of height sliding doors are generally the same height as equivalent conventional doors (so often about 6ft 6in or 1980mm). What you will need to determine, though, is the type of wall they are going into - is it a stud wall or is it solid masonry, and if so is it load bearing? For a masonry wall or any form of load bearing wall it will be necessary to install a universal beam (UB) or concrete lintel(s) above the opening - if the doors are the type which disappear into pockets in the wall then the UB or lintel(s) will need to span the full width of the opening, together with the width of both the pockets (into which the doors slide). This may well require the services of a structural engineer to do the calcs for you on sizes, bearing areas, etc. I'd recommend that you Google sliding doors to see what's available, then maybe come back with some more specific queries, if you have any
In other words I feel that there is no simple answer to your question and that before you consider the door style you want you really need to get the structural aspects of this sorted out. That way you'll be able to get a handle on cost and feasibility, etc
