There's an International Violin mandolin kit waiting to be completed in my shop. It looks decent enough though the fingerboard will be replaced with a radiused ebony one. I am waiting for the humidity to stabilize for the winter before starting.

I once assembled a harp kit for a friend and it was the worst experience. Nothing was measured correctly, and the woods were not fully dried.

Grizzly (www.grizzly.com) has kits and an online catalogue. The mandolin neck join looks suspect but many of their parts are good.

Good luck.

Peace, Mooh.