'What if'

What if I had something big?

1) What will you do if I had something big?----------------Wrong?

2) What would you do if I had something big?------ Right

What if I have something big?

3) What will you do if I have something big?--------Right

4) What would you do if I have something big?------Right?


I think that #1 is not possible but #4 can be okay because I can see many sentences like 'If you do not mind, I would like...', but come to think of it, we also can see sentences like 'I am sorry if I did...' Whether meanings of them are somewhat awkward or not, I think all of the sentences are possible forms. What do you think? Thank you so much.