There are few interviews where designers mention anything significant in particular about Shiva. However, you can view their storyboard sketches for Shiva's animations in visual guide books released for the games.

Yoshitaka Amano
Yoshitaka Amano was born in 1952, he joined Squaresoft in 1986 doing concept art for Final Fantasy. He designed Shiva for FF3-6 and image illustrated for 9. He also created designs for the games Front Mission, Gun Hazard, Rebus (aka Kartia) and Emblem of Eru.

Tetsuya Nomura
Tetsuya Nomura was born in 1970 he joined Squaresoft in 1991. His major debut was doing easily adaptable character designs for Final Fantasy 7. He designed Shiva for FF7-8. He also created designs for the games Parasite Eve Series, Brave Fencer Musashi, Dewprism (aka Threads of Fate), The Bouncer and Kingdom Hearts.

Akihiko Yoshida
Akihiko Yoshida was born in 1967 and joined Squaresoft in 1995. FFT and FFTA's Shivas are beautiful, intricate artworks. This designer is one of my favorites, save the overuse of earthy tones! You can see his art (again, not just characters) in Vagrant Story, The Legend of Ogre Battle and FF12.

Yuusuke Naora & Tomohiro Kayano
In the 3D games both Naora and Kayano add to the art and creation of Shiva. Naora is the art director and Kayano is the real time polygon director. Naora works on the artistic details while the transition to 3D is done by Kayano's skins. Naora also created the design for FF10's Shiva.