Sump pits are intended to collect water from foundation perimeter drains. If there is a pump installed in the pit and no water is collecting in the pit, be sure to check the pump to be sure it is working. The easiest way to test your pump is to fill the sump pit to the point it will activate the pump, if the pump does not work replace it.
Most greenhouses have frames of wood or aluminum. Wood will lose no significant heat through the frame. Over time the wood fades unless you keep it painted or finished, and it may rot or warp. Aluminum frames retain shape well, won’t corrode, and are often color-coated. Some heat is lost through the aluminum.