Simple to construct marking gauge from walnut & holly. The only in-progress photo but a plan is included.
A marking gauge has four main parts: fence, beam, thumbscrew, and a blade or pin. The four piece beam makes this gauge simpler to construct. Here it is three pieces of 1/4 x 5/8 walnut and one piece of 1/4 x 5/8 x 3/4 holly. Screws into end grain tend to strip so the holly is rotated 90°.
The fence can be one piece but I inlaid a strip of holly for wear resistance and because it looks nice. [note: the plan above has an error showing the holly wear strip on the wrong side of the fence] A hole is drill about 1" back from the fence for a 1/4x20 threaded insert. Thumbscrews can be purchased or shop made, I made mine from a 1/4x20 bolt and walnut scrap. The blade is an old jigsaw blade, the type attached with a screw, snapped off and sharpened a bit below the screw hole.
The blade was scored with a file, pinched in a vise along the score line then snapped. Watch your eyes.