Yes, you have time to really design what you want, what will be safe for the animal, & sturdy for many years to come. And able to be moved, for sure.
As I thought about the greenhouse you thought about buying, I just remembered how metal sheds always are too- on the inside, where people can't/won't reach, there's always sharp edges exposed. They don't finish such things because it saves money- if they want to sell their product, the cost has to be competitive with other similar things on the market.
You weren't wrong to "think outside the box" for something you could easily repurpose for a snake home, but you always have to be on guard so you don't overlook design flaws- things that don't matter when products are used as intended, but things that can be very unsafe for your (our) purposes in keeping animals.