I'm a stonemason and slater to trade, the Scottish traditional slaters worked freehand using all sizes of slate widths and lengths.
The first course consisted of the smallest lengths(under easings)followed by the longest lengths to form one watertight course.
We work up the roof in diminishing lengths to the ridge where we terminate with "The Wee Toppers".

Slaters are always pleased to see the "Wee Toppers", from whence comes the well known Scottish saying....."Yer a wee topper"