Deep, gruff, jowly, with a unique accent (German, Greek, Middle Eastern, Welsh, etc - essentially just avoiding existing represented accents of British, American, French, Polish, Russian), to highlight his isolation and uniqueness in the world as the last Dwemer.
We are also leaning away from Scottish accents - the original Morrowind team went out of their way to differentiate the Dwemer from the standard fantasy dwarves, which often use Scottish accents, and we're trying to honour that vision. 

The Dwemer have some Babylon/Persia inspirations in their background, so accents influenced by these cultures, and Semitic accents, are encouraged.

Additionally, Yagrum is very sick - so going with a strained, phlemgy emphysemic delivery would match his outward appearance.

Yagrum Bagarn is a resident of the Corprusarium and the last known living Dwemer. He is infected with Corprus, and can only move around with the help of a modified Centurion Spider's lower half. He is a good friend of Divayth Fyr, a powerful and ancient mage who oversees the Corprusarium and Tel Fyr. Yagrum is also the author of Tamrielic Lore.