its easy 1st things - 1st you need to look for a good yilding plant not just any old shity thing i.e look at it like this lets say you grow 10 plants, the worst plant yeilds 1oz dry the best yeilds 1.5 oz dry< more about this in a bit.
the method you need to use is called SOG (search it) you grow lots of small cuttings from clone you veg very little 3 - 14 days ? then you flip them in to flower you want to plant out at 1 plant every 6" or 4 per squre foot untill 1/2 your room his full you do the same the other side in 4 weeks time and harvest there after every 4 weeks. the plants should yeild avarage 1oz each now here is where the best yeilding mother out of the 10 plants you grew above comes in to play.
under a 1000w in a room 4x4 (no bigger!) you can fit 64 small clones or in both rooms your total will be 128 clones. work on just 1 room for a sec then just X'2 for toyal every 8 weeks. this is only an example to give you an idea why you need the best yeilding clone you can find.
64 clones at 1oz = 64oz per room
64 clones at 1.5oz = 96oz per room
it does not work like that, but if you pick the best yeilding plant over all you will yeild 1/3rd more than if you picked a shit mother to clone from. under a 1000w lamp 1gpw or 2.2lb is very easy to do if you find a good yeilding plant and grow using SOG even more 9-) now if you use the shit clone then you are looking at around 750g in the example above.
so all in all 2.2lb every 4 weeks = 4.4lb under 2000w of light is very doable if you pick the corect high yeilding clone and SOG the best iv done was 1.25gpw or 750g under 1x600w HPS.