Should be with 〜べきだ
Grammar: Necessity » 〜べき
Adding べき to the end of a sentence gives the meaning that the speaker believes someone should do something, or something should be in some state.
When used as an auxiliary, べき is followed by だ. Changes in tense and negation are done to this だ.
If べき preceeds a noun, だ is omitted. On the way home from shopping, it starts raining.Further Reading
Examples
Should have brought an umbrella with 〜べきだった
