Tefillin consists of two main parts: the ketzitza (קציצה) and the titura (תיתורא). The ketzitza is shaped like a cube and consists of four capsules (בתים). It sits on top of a platform called the titura, this piece of leather seals the bottom of the ketzitza, after the parshiyos have been inserted in the capsules, and is sewn together with the upper part.
I want to know if the titura and ketzitza are two seperate piceces of leather, or one piece? From what i understand it is one long piece of leather that folds over, the folded piece becomes the titura and the upper part becomes the ketzitza. I want to know if my understanding is correct (sources please), and if halacha dictates any of this?