If you’re not building a passive or showcase-only wine cellar you will need to buy a cooling unit for your space. Cooling units keep your wine cellars at the correct storage temperature and humidity (~55°F and 50-70% humidity).
The first thing you should splurge on in your wine cellar is the cooling unit. It might be tempting to undersize your cooling unit to save a couple dollars, however this temptation usually results in a unit running loudly 24/7, unable to get your cellar to 55° and dying early from exhaustion. In ideal conditions your cooling unit can last up to 15 years but an overworked unit can die as quickly as 5 years.