Wards protect against magic, but without perks they spend an awful lot of magicka. Best protection against dragons would be
1. Stay out of their breath

2. Enchantments: Resist Fire, Resist Frost, Resist Magic
3. Potions with resist frost/fire - collect lots of snowberries that protects against both, and combine with one ingresient against fire and one against frost, that way you get a nice combo-potion you can down even before you know which breath the dragon will use. Combine with Resist magic potions.
Stoneflesh and a ward on top of that, and some ranged magic or a staff, and you'll be fine. Even better with a follower. (I love it when dragons attack at the CoW courtyard. Once I didn't even have time to attack it myself before it was dead, killed by three wizards and their summons.

)