I got the colt oem2 I love it, the 875 Nordic sale price is a smokin deal. Mine was 900 on Black Friday saleS.
...But if you want to build it yourself and add a handguard and all that you will need a few tools like a strong vise, hammer, reaction rod(I think cgn retailer has unbranded rods for under 80$ Or real avid) or vise block and some roll pin punches for the gas block/ gas tube a really strong punch for the gas block (I used a strong bolt as my punch was mushrooming)retaining pins and a wrench for the barrel nut, you can get a cheap wrench for around 30-40$.
Roll pin punches and roll pin starter punches cab be bad for around 20-60 for a full set but you only really need like 3 sizes for an ar.
Then you will need a handguard and stock to finish the build.
I know tenda and a few retailers have a little nc/star ar armorers kit for like 75$ not sure of the quality as I have not used it.