Construct an irregular tetrahedron

What method should I use to construct an irregular tetrahedron? I.e. how do I choose angles and edge lengths so that they come together as a tetrahedron? How do I formulate the restrictions that define a tetrahedron?

Only restriction I've found on the net concerns 6 of the angles:

OAB*OBC*OCA=OAC*OCB*OBA

Of course, some of angles in each triangle = 180 is another restriction. But it's not enough.

Btw, there is terribly litte info about irregular tetrahedrons on the web.

Thanks for any help!