Lawn Care Pricing

I have always wanted to own my own business and after long and careful consideration, I have chosen lawn care. Lawn care is one of the best businesses to get into currently from what I've been reading and I enjoy doing it. Over the past few months my business hasn't been "official" I have had a couple job here and there, but haven't gone all in. I am here because I am writing my business plan and I am unsure about pricing. I have asked a few different people and some say I should charge hourly, by the square foot, or even a flat rate (I don't like flat rate). I was thinking I would charge by the square foot because it seems the pay would more closely reflect the amount of work. I was thinking I would charge $.004 - .005/1 sq ft. So for example my first customer who's yard is 15000 square feet would cost $60 - $75.

Some professional opinion and advice would be much appreciated thanks!