If I finish the dress before Monday, I will give it to my sister
⇒ Should I finish the dress before Monday, I'll give it to my sister.
If you see Peter, tell him he should be there at five.
(Cái này là If rồi, thì viết lại câu phải là Should chứ nhỉ....?)
⇒ Should you see peter, tell him he should be here at 8.0..