I approve of the refurbishment of Canonbury station but the ticket office looks like a concrete shed thrown up in the 1950s. I was wondering where the original ticket office had been because the present one clearly isn't it. Anyway it was obvious which building it had been when I left the station and turned to my left.
Here's a somewhat wonky line drawing of it. I think it's a rather handsome building - the three large windows on the ground floor could have been where you bought your train ticket from. And I wondered if there was a waiting room behind the door on the left? Well I can only speculate about its previous use because it's now been turned into a small block of flats (that's handy for the station).