you typically want one square foot of floor space per foot of snake. Therefore a 4 x 2 is good for an 8 foot snake. You want to watch the height aspect, the taller it is, the harder it is to keep the temps and humidity up. When I bred boas we kept them in cages that were 4 foot long, 2 foot deep, 15 inches high. You also want to avoid any exposed wood as it kills humidity. Melamine is a good choice for a cage material, though it's heavy. You can look in the caging section at my thread for DIY cages I built for my retics to get some ides on ventilation and such. The more ventilation you have, the harder it is to keep the heat and humidity in as well. Also, belly heat is definately the way to go. no heat lights.
