Thanks!
RL worms its way into art. As a part of my histrenactment hobby, I make my own costumes, and thus know something about actual historical patterns and how fitting works. Since I've adopted a distinctly Viking-inspired style for the Giants, I can use my existing knowledge here.
1. "Patchwork" clothing was common in Ye Oldendays, and the cut had less to do with the status than the dyes/materials/weave (compare vaðmál to silk). See the
Viborg Shirt. Weaving as much fabric as required in a
Finnish Viking woman's peplos (or overdress) with a warp weighed loom took a year from one person, and thus canvas was never squandered. Every corner became used somewhere in the sark or dress.
Naturally a Giant's garment would require oodles of more fabric, a thicker weave (more expensive to make), or possibly several layers of said material. We've read about stone mail, leather, but also a knowledge of wool weaving/knitting in TOT, which implies they probably use a variety of different materials for their habiliments. And a pair of linen braies sounds more comfortable than interlocking granite discs.
2. Normal shirt cuts wouldn't sit at all with his awkward body, and I don't see why he ought to wear one of those elohim muumuus either.

Stitching together pre-cut "patches" or making copious amounts of sisennys (not sure what it's called in English, a handicraft term nonetheless) is the only means to sew him a nice sark/jerkin.