You should buy a case, or a gigbag for your ukulele, if it has a standard size and shape. I made some ukuleles with uncommon body shapes, or I combined a concert size neck with a soprano size body. It was always difficult to find cases for these instruments. My homemade ukulele with its side-mounted tuners also won’t fit a standard case. Someone who succeeded to handcraft a ukulele will find it easy to make a case.
 

Step 1: Cut the wood

• Cut the wood. Cheap plywood works fine for a case.
• Glue the body and the hood
• Enforce the case body and hood with linings

Step 2: Glue leather on the case

• Use carpet glue to glue plastic (artificial leather) on the body and hood

Step 3: Assembly

• Assemble the case (joints, handle etc.). It makes sense to add some protection for the edges and corners.