But I think I will put a heater In there cause I want them to lay eggs when there is no sun
A heater is different than supplementary lighting. Go ahead and put a light bulb in the coop--if you set it on a timer, you can have it come on very early in the morning to make sure that they get at least 14 hours of light per day. It's best to use supplementary lighting in the morning rather than at night because when the lights go off abruptly at night many hens haven't had a chance to get to their perches, etc.
But a heater is there to make the hen house warm, not to light it, and a heater will not get you more eggs. A heater might get you sick birds, though.