Help! What tank is best for a Corn Snake?

[AwakeSnake]

Not sure if this is the place to ask, however, I need some advice.
I really want a corn snake and have done LOTS of research so I know how to set up a viv and what temp to keep them at etc. etc. though I haven't been able to find anything on what the best type of vivariums are. Even though they are very cheap I don't want a plastic tub as I don't think it would be good for the snake, I would also be paranoid about it melting the plastic even though I'm sure that wouldn't happen. Would a fish tank be best or get a proper viv? I want something simple and I'm quite hesitant to go for a normal vivarium with wooden on the base as I've heard you need allsorts of seemingly complicated stuff like thermal blocks so it doesn't set alight. Also I feel like a glass one would be slightly raised so the heat mat wouldn't be touching the surface that your tank is on. Also what size? Is 4ft big enough for an adult or does it need bigger? If I got a fish tank I know the min size is 20 gallons for an adult corn but would it better to go for a 30 gallon? Lastly would it be better to have something higher and narrow,(I know corns like to climb) or long and low (but still with branches and places it can climb and wrap itself around). I just want something reasonably cheap, uncomplicated and what's best for the snake. Please could I have some advice on what you think is best!