Beware of green tea if you are on a blood-thinning medication like Coumadin, commonly used in cardiovascular conditions. My neighbor, in the hospital, was swigging green tea because she had lived in Japan and swore by it. Meanwhile the docs couldn't get her Coumadin level adjusted---she kept bleeding where she shouldn't. Turns out that green tea potentiates (reinforces, makes stronger) anti-clotting medications like Coumadin.
I can't imagine that anyone could drink more green tea than me. I drink it hot, I drink it cold; I'll whip up some matcha. That being said, in all the years I have drunk copious amounts of green tea, I have never noticed any health benefits from it. It doesn't particularly energize me, doesn't help me concentrate and it certainly has never helped me to lose weight. I just happen to drink the stuff because I love it. Not sure why you want to go on a "green tea diet" or what you hope to gain from it.
I am really pushing up my green tea intake this year. I find that I drink more when I make it as iced tea. I drink more when it is ready to go:
I keep green iced tea in the fridge, usually decalf so I can drink it at night. I like to mix decalf and detox tea together with a drop or two of stevia and keep a few different flavor mixes in there, ready to sip.
Also, in the morning, I fill up my stainless water bottle with water, ice cubes a few drops of stevia and a green tea bag. By lunch, the tea is "brewed" and ice has mostly melted.
I have been getting about 4 to 6 cups of green tea a day this way.