Which welder do you have? Do you have nickel shears or a corner chomper? Do you have empty practice cells? Do you have a multimeter? Which lipos are you using for your welder? What are you using to charge them? Have you sourced nickel? Have you tested it for purity?
There are a LOT of things you need and it’s not really feasible to learn to do all this and invest in all the tools just to build one copy.
Buying a battery from a reputable builder is a really good idea.