If you've got the space for a car sized one then you've pretty much got the space for a proper garage. 
 
  
Wouldn't need planning permission for it, as its not a permanent structure.  
  
Wrong , even an awning needs permission 
 
  
A commercial awning also needs building regulations so as to make sure it doesn't fall on somebody's head..  
  
A awning on a private residence doesn't..!! (maybe it depends on which Counsel you are dealing with)..  
 
  
Check with your local Council - planning rules can be complex.  Being a ex-planner it never ceased to amaze me the various interpretations that can be made from one local authority to another and a lot depends just whereabouts on the house it would be sited and what local controls may have taken away normal permitted rights normally expected.  But a bit extreme to seek Counsel advice Will  
 
  
No I didn't say you need Council advice...maybe building regs for a commercial one. ..it was richf who said 
  
I was talking boll**cks  
  
Quote : Wouldn't need planning permission for it, as its not a permanent structure.  (Will)  
Wrong , even an awning needs permission (richf).