Solas will be your barrier/support mage. Thus he is simple to build:
- Get about everything in Spirit. You can decide yourself if the mana/stamina regen and revive is worth it, but I take it anyways.
- Winter's grasp and the passive to the left of it(the name escapes me now..). Later on you can also grab the mana-on-stand-still passive and Fade Step.
- About everything in Rift mage. Weakness is huge, more mana is huge, control is huge.
- You could get Energy Barrage for more dps, or go down fire as well. Your preference. Spirit/Frost/Rift Mage is the core/defensive.
His most important abilities are:
1) Barrier. 'duh!
2) Winter's grasp. CC and set up combos.
3) Dispel. Dispel is love, dispel is life!
4) Veilstrike or Stone*whateveritis*. Rift mage abilities for weakness debuff.
Everything else is optional. Just remember to reserve his mana at 30%/50% so he don't spend mana dpsing, when you'd need it for barrier, winter's grasp or dispel!