There's some page that has voxels for certain doom items and enemies IIRC, I'll try to post the link here <!-- s:) --><img src="{SMILIES_PATH}/icon_smile.gif" alt=":)" title="Smile" /><!-- s:) -->.
I really don't know if the doom engine would handle voxels, but I remember I saw someone trying to add support for it with not very good results <!-- s:) --><img src="{SMILIES_PATH}/icon_smile.gif" alt=":)" title="Smile" /><!-- s:) -->.