You must be a Wizard with the school of Abjuration Arcane Tradition.

You expand your Arcane Ward to its furthest limit (10-foot radius) and choose the type of elemental damage to absorb (fire, cold, acid, poison, Lightning, and Thunder.) Then roll an Intelligence check with a DC of 20 minus your INT modifier. On a success, your ward had resistance to the specified damage type and absorbs as much as it can within its radius, but takes full damage from other elemental damage types and lasts until the start of your next turn, or if the ward reaches 0 hit points. On a failure, the ward does not have resistance and takes full damage from any elemental damage type. If the ward's health is reduced to 0, the remaining damage will hit the affected target(s).

The dome has the normal amount of hit points that the Arcane Ward would have, but also gains the hit points that casting this spell would add to the ward as an additional buffer. Any excess hit points from casting this spell that are left after the spell ends are lost.

The wards outermost limit increases by 10 feet for each spell level above 4th that is used to cast it.