How many solar panels do I need to power my two bedroom townhouse?

I have a 2 bedroom townhouse in Arizona and I am wondering how many solar panels do I need to get so I can disconnect from the main power system and never have another electricity bill.

If I look at my utility bills over the last year I can see how much electricity I have used, do I just use that figure to work out how many solar panels I need?

Are solar panels the only thing I need to buy and do I have to put them on the roof, won't all the extra weight cause problems for my roof?