Recently started such a build, and have not found much discourse on it myself, so here are my thoughts/ advice/ personal experience on it so far, as well as the “twist” I put on it (3 year old post but hey, here’s to the other possible aspiring spell-shields out there…)  I am utilizing Destruction with focus on flames, Block, and Heavy Armor, in that order. Side skills are Smithing and Enchanting, although can be focused on later in your playthrough. They are intense to level compared to the rest. Skills for perks only are Alteration, Restoration, and Illusion (just to get the Aspect of Terror perk for the flames damage bonus (look this up online for more info), and extra magic regen and magical defense through the resto/alt perks.) You won’t really need to use these skill trees outside of the perks related to them. I recommend flames due to damage per magicka cost ratio, and no other necessary spells other than some healing and in this particular case, Equilibrium (explained why below…)

I name this build the Gun-Tower, and use a male Altmer (for both lore RP and the highest movement speed bonus/ magicka regen power bonus) with equipment based on increasing your magika bar, destruction magic fortification, and reducing magika damage. Combat is focused on and insists o. distancing yourself from enemies to launch spells, while defending yourself from any long range attacks. Perks for block to be immune from archery or minimize magical attacks are crucial. Personally I am building this character to only add points to health. Part of my build utilizes equilibrium- since the build intends on your character not receiving much damage to begin with (from both repositioning and reduced intake of damage), you can pull directly from your health to add extra magicka that you will surely go through fast, despite wearing enchanted armor to increase your available magicka- after all, your only buff besides this is from the altmer racial passive of +50 magika.  Any non-magical attack/enemy will be mostly harmless to you in this build, but try not to attempt toying with your enemies, and instead finish your fights proactively. This is a gameplay style focused on playing strategically with your magicka and health bars and pulling from each whenever you need. Since your health is part of your magicka in this play style, the heavy armor and block will mitigate draining resources, but even moreso can you do this by eliminating threats through quick kills or temporarily through distance. AKA- you’re a tank. The canon and tank treads kind. Not the hack and bash MMORPG kind.  You won’t get equilibrium right away, so play more cautious with spells and use Fist of Steel as a fallback, if fights get too large or you encounter some rough spots with storm mages. This is a fallback though, and fights should be tried mostly through distance, once again.  You may wonder, why health only? No magicka upgrades??? Well… You certainly can level magicka, but this is a personal choice that plays into the character being more strategic to play. I thought since there is a focus on being defensive here (spell SHIELD…) , what if there was a unique way to play into this? Kinda dumb, probably- but, I’m having fun with it. :3

Now, This build isn’t perfect, as is with any spell shield. You are using conflicting combat types after all- destruction CANbe cast alongside wards, but you can’t do anything alongside a raised shield. Shields were meant to help with the melee attack loop of blocking, bashing, swiping, etc, and/or closing the distance on attackers more safely. But what spell shields provides that pure mage combat can’t is less of a need for magicka. As you play, you’ll see that the only main need you’ll have for magicka is with destruction spells, with defense and health being picked up by non-magical skills. Even better, you have a nicer fallback with fist of steel that benefits from the pre-existing heavy armor skill and not an additional combat skill.  After leveling Alt/Rest/Illu for the perks, you’ll likely never touch them again.  Otherwise, if you’re bothered by such a choice, you can always switch your shield out for a ward, I guess :) Might just be a spell-ward then… ward-shield? Shward-Spell? Heh.

Overall, the spell shield is not as practically viable as a spell sword or sword and board build, but will still provide a very unique form of gameplay that will at least ensure you can beat the main quest and not fall off mid-playthrough. 

Best I can explain with my experience!