Cutting out. The best way to cut out a sheepskin is to take it from the centre of the skin to ensure an even thickness throughout the bag. Some sheepskins are large enough to get two good bags out of it but you need to examine the thickness of the skin carefully. Generally speaking, skins tend to get thinner towards the edges and you want to avoid ending up with bags that have areas which are particularly thin.
The bag I'm showing here is a standard medium size, ie. 11" deep (folded, before stitching) at the centre and 28" long. I have also cut out the two strips which will form the welt and gusset. They both need to be at least 39" long. The gusset is 7/8" wide and the welt 2" wide.
The shape of the bag can vary from maker to maker. This is the standard pattern I have always used. I have a range of cardboard templates for various sizes. The important measurement that never varies is the chanter stock end. When finished the neck should be exactly 2.5" wide measured across the neck to the line of stitching. So you need to allow 6" when cutting out the skin.
NB. Always examine the inside (smooth side) carefully for minute punctures or defects which might cause the bag to leak or fail prematurely.
(Clicking on some pictures will give a full size view).