Hi
The above post is correct, sort of. If you can create the 3D element by extruding a polyling or region, the mass properties command will work. So for relatively simple shapes, you can easily create the 3D element inside autocad. More complex shapes would be tedious to create in CAD, but could still be done.
Not knowing what your object looks like, but going on "lines and 3d face object", it should be possible to assemble the 3d solid by extruding the faces and combining them to form the product you want.
Hopes this helps.
One further tip I have found using mass properties. If you move the item so that its centroid is located at 0,0,0 you will find that the principle moments equal the moment of inertia about the centroid. This makes it a little easier to know for sure which is the correct moment to use. At least I think so, but I may not know exactly what all the various properties mean. Usually I want the moment of inertia bent about the neutral axis for structural purposes. But others may want other moments about a reference axis for other reasons.