For clarification: Our contractor is asking us to find a threshold that is 6" wide x 60" long. Do we need one solid piece of marble or should we buy pieces for him to fit together to form threshold? We are having trouble finding anything that long and wide and are asking for help/suggestions. Thanks!

Standard size is 36" long. Most pre fab thresholds are made for doorways not showers so this is why your having a hard time finding one. You can contact a stone fabricator and they'll cut custom sizes for you. Using two pieces might lead to mismatched color or pattern unless cut from the same slab.

Enjoy your shower! I'm sure it's going to look great!