FWIW - when I did my sums recently on owning/renting for a 4 seat light aircraft with no loan costs, it worked out to be I would need to put 200hrs/year on it before buying beat renting.
That number would be better if you had lower hangar fees than typical Sydney basin or if you were happy for the aircraft to be parked outside.
Those figures depend a lot on aircraft type and hangarage, and also to some extent location (think movement charges, fuel costs etc) but I worked out 200 hours was a roughly the balance point for me and my aircraft choices.
I was expecting fuel to be a big factor but was surprised how hangarage in Sydney (BK/CN) also made a big dent on costs/hour.
I did the calcs for my choices and situation by setting up a quick spreadsheet, looked at approx maintenance budget for engine/airframe spread over typical rebuild times, 100 hourlys, refurbs etc plus fuel costs, hangar costs, insurance, movement charges etc to get an hourly rate it was costing me to feed and water the aircraft.
The more hours I did, the more it dropped the hourly costs (basically the more hours would reduce the impact of the fixed costs). As I said, I found around 200 hours/year it started to look cheaper to buy than rent - depending a bit on aircraft type.
Other factors that you might want to consider when working it out would be if you were needing finance, if there were any tax deductability options, maybe putting it on line to offset costs etc.