Jean button X-kilt?

[vorpallemur]

That would be a lot of material to do a buttonhole through. You could have 6 or 7 layers to go through depending on how you do the waistband. I would test it with your machine. If you are using a machine to do the button holes. Also if your waistline goes up and down, you might want to consider multiple buttonholes.

Let us know how it comes out. And post some pics.

How many layers they go through depends on where he's planning on putting them. If they're on the apron, it's only going to be a couple of layers, at least on the right hand edge. On the left side of the apron, there's an under pleat, so it would be a bit more. But not too bad. If it's on the waistband, it depends on how the waistband is done. If the skirt^Wpleated bit is hanging from the waistband, then the waistband is just two layers, plus whatever is being used to keep it from rolling. If it's done like the x-kilt instructions, it's also going through the pleats.

I'd suggest making a basic, per instructions X-klilt or traditional kilt first, before trying to do this. (Unless you've got lots of garment design experience, or a high frustration tolerance.) Once you've done that, you'll have a better understanding of how and where you'd put the buttons.