@turboizak You're underestimating your rent.
600 p/w is closer to 2600 p/m as a month isn't 4 weeks.
So total rental expense is shy about 31,600.
Also are you including tax in your 8% growth stock portfolio? Stock returns are generally split into capital growth and dividends. The dividends will be taxed. This could easily bring 8% down to 7%.
Another issue is that your monthly outflow of cash in rent scenario will increase each year assuming fixed investment amount and a growing rent. To compare the two scenarios you need to keep monthly cash flows the same. So you'll need to increase the amount you invest per month each year in the "buy" scenario to keep up with the rising rent in the "rent" scenario.
Your analysis would be better if you looked at a range of possibilities.
I would start with the assumption that returns on both are equal and then find condition under which one out performs the other and ask yourself how likely that is.
Edt: oh man every time I look at this I see something. So to calculate your net investment gain you've calculated your net gain on your 350k investment but you're using your gross result for your monthly investments. To get net you need to subtract and additional 360k from the total.
Also the way you're calculating the interest on your monthly investments is wrong. If the stocks return 8%per annum that is not .08/12 % per month. This inflates your stock returns by about .3% per year which adds up.