If it's your first build, do yourself a favor and buy the kit. Everything HBP said is entirely correct. If you've never built an amp before; unless (as he said) you have all the screws and star washers and spacers and fuseposts and cable clamps and tie wraps lying around...and have to order them in....that stuff will kill you.
When I started building, it was many years ago...and I don't say that to say I've built hundreds of amps...there was 20 years when I didn't build any. But parts were cheap and there were lots of surplus places which I loved to dig through where I could get *some* parts. Whether I ever saved a dime buying those surplus parts I could is questionable, but I liked to scrounge, and I lived near NYC where I could go scrounge on Radio Row/Canal St, where the WTC is. There were blocks and blocks of electronics surplus joints that I loved to rummage around in.
Now there's hardly any of that any more, and because of ebay, every idiot knows that pots sell for $3, not 25 cents like they used to. So there is very little advantage to sourcing your parts a la carte. Not to mention leaving some out and having to order and reorder and pay freight every time. Back then, there were many, many parts that were 25 cents and fifty cents each. Now, there's essentially no part in the amp other than a few resistors and some screws that cost that little.
The other aspect is that the odds of you successfully completing the job and having something that works, for your time and money, is 20 to 50 times better with a kit. The downside of "no kit" is that you have a $200-$300 piece of useless crud sitting on your shelf for years and years and eventually throw it out or give it away. Plus the task of getting nice big holes (or even small ones) in a sturdy piece of metal, all in a line and nicely spaced, is not trivial if you don't have decent tools. In the end, maybe you'll save $50 buying the parts one by one but if you don't end up with a working usable amp, you have a big fat zero. For $50 more, you have a clear road to something you want. If you were experienced, I'd encourage you every which way, but you're not.
Buy a kit.
Y'know what blows me away? The price of spacers/standoffs. I used to work in a factory that threw out more of them in a week that I've ever used in my entire building career. I had coffee cans of 'em. All tossed.