Sorry for the necro, but....

When I've had to make a mold of something real, I've scanned it on a flatbed scanner, with a high precision ruler next to it.

I then import the jpg into sketchup and scale the image to match the ruler. Make sure you only grab the corner, or else it will only scale in one dimension.

Zoom in real tight on your object and using the line draw (pencil) trace the outline of the object. Then scale that up your desired amount so the object will fit inside of it.

Place the new object on top of the extruded base of your case, then extrude the rest up. Viola, pliers case.

Takes me about 20 minutes to get the object shape into sketchup, then just a few minutes more to finish the item.