How Big?

Just wondering how big roughly should a plant be after 4weeks of veg from seed? Like height wise?

Depends if you're growing outdoors or indoors. Using my own situation as a referance, my plants were about 6 inches at that time. I grow indoors using hydro with a 600w HID. Heat was a real problem for the first couple of weeks so their growth was stunted a little. At one month they should have been a good 10-12" at least under optimal temperatures(70-85 degrees). I don't imagine a plant being more than 6" tall from seed after one month if grown outdoors, but it's possible.