i'm guessing you want to run it from 12V. so you have a source of 12V @ 100A, plenty of 00ga wire, a bank of MOSFETs than can safely chop 100A, and an appropriate transformer which would be a 12Vct@100A winding and a 120V @ 10A or a 240V @ 5A winding?
excuse me if i sound cranky about this, but why does everybody want a 1kW inverter right off the bat? try building a 100W one first then look at it as a matter of scale (do i really want to try something 10 times as big? and 10 times as heavy? and 50 times more expensive?)
look inside a 1kW UPS supply. that will tell you a lot about what you're up against. those are usually run from 24V or 48V batteries for a reason, which is the current requirements of the transistors and transformer.