And a disagreement with some of the posts above FWIW.
I don't know your construction constraints. If you're carving your cellar out of mountain rock, then the size really matters. But if you're making a space in a basement or something of that nature, bigger or smaller isn't really going to make a big difference.
So I'd make it 20 or 30 times what you thought you want.
If you have say, 20 bottles of wine, doubling your space gives you 40. If you have 100, doubling your space gives you 200. There's no point in building a cellar if you're going to store only that many bottles. You're better off buying a wine fridge.
You store wine because you want it to mature and improve. If not, just buy the current vintage. So if you're going to store your wine, do you want to store a dozen bottles for 20 years and then start again? Makes no sense.
So if you're building, build something that can store a thousand or two or three or four or more bottles. The cost isn't really all that much different, unless you really trick it out and make custom racks etc. But that makes zero sense to me. I have a fridge for food. I don't spend time inside of it or open it to stare lovingly at the contents. Same with a wine cellar. It's a storage closet. So make it big.
And remember, you don't have to fill it and you don't have to use it exclusively for wine. You can store fruit or meat or whatever in there if you have too much space. Cool storage is always useful.