Is it possible to construct a 3D molecular model using x-ray powder diffraction data?
What do you hope to achieve?  It is possible to obtain accurate interatomic distances from powder data (here is an example, the structures of several alkali metal cyclopentadienides), but the method is non-routine, and the data-parameter ratio is low, which means that you cannot refine many parameters and must put much information in through appropiate restraints.  You still need accurate peak shape data.

If you just want the general shape of the molecule to illustrate Wikipedia, you are better off with obgen from the OpenBabel project.  It usually gives good results.