There are two basic kinds of dealer item silk foundations.......those utilizing complete silks and those employing the sewn, half silks.
The advantage of the latter is that it saves you time folding & when opening, the display appears to produce twice as many silks, albeit smaller, half size silks.
I prefer the latter for small rooms....same effect and can be seen. However, for larger venues the whole silks can be seen better.
You can also purchase silk cranks/rollers which save you time in preparing & they compress the silks far better than you can by hand, thus enabling you to load many more silks than you might otherwise be able to employ. A simple folding of all four squares into the middle, holding the pinch by either hand or gimmick will suffice.
If sewing half silks, then obviously only sew on the "bottom" two sides.
In addition to Tarbell & Rice's Silk Encyclopedia you can call Pete White and other silk mavens....unless I had a bundle of beautiful, fresh, virtually never used, 100% Rice quality silks....frankly, rather than starting from scratch preparing my own....probably better off purchasing a Magic Hands/General Grant/White/Hank Lee etc. already prepared dealer item.