Cage size controversy

Hello all:
I have kept reptiles for many years and i now have decided to get a large snake, about 6 feet, and make a cage for it. I am going between a dumerils boa, red tailed boa, rainbow boa, or carpet python. Everywhere i look i hear different oppinions on cage sizes. Some people say the snake needs enough room to stretch out completly and some say that a cage can be as small to allow the snake to get in and out of a warm spot. Many breederes keep large snakes up to 7 feet in small 3 ft by 4 foot by 1 foot tall. Any opinions on cage sizes for six foot snakes? I want to build a cage that can pretty much accomidate any of these species in case i change my mind or am unable to find a particular snake. I have been looking at the vision cage V400. It is 48" by 26" by 14" tall. What do you think about the highth? even though a lot of snakes are classified as arboreal, as adults they don't always climb. I guess my question is....What is the minimum size cage that can pretty much accomodate any 6 foot boa or python and is vertical space as important for the larger arboreal species?