What's the best way to phrase "没事是......做什么?" in english? I found that that form of phrase is used quite often.
I thought it could be read as "What are you being .... for?".
But I'm still confused about the use of '没事' here and how to properly put it in English.
Do you mean “没事…做什?" If it is the case, then  没事 is short for '没事要做 (without thing that has to be done); or 没事發生(nothing has happened) 


  没事 means 'for no reason' or 'with no purpose' in this structure.


For example: 

"没事回來做什?" (for no reason, come back for what?/ why come back for no reason?)

"没事去看醫生做什?" (for no reason, go to see the doctor for what?/ why go see the doctor for no reason?) 


  It should be' 没事...作什', but '没事...做什?' is also valid because 做 is the modern counterpart of 作 in classical writting for the verb 'to do'