I know those have been done a lot, but i didn't seen some sprite of those game so here we go, those skin contain custom voice and crouched sprites for the Build games ones.
Fighter, Cleric and Mage from HeXen
LoWang from Shadow Warrior 1997 and Caleb from Blood
I made 2 versions of those skins, one for Doom (skin4D) and one for Heretic (skin4HT), the Heretic skins is buggy on doom but the Doom skins work on both game, but give disappointing color.
Ingames Screenshots:
Doom
Heretic
Download link (BD stand for Build game and HX for HeXen)