I tie my own knotted leaders for bass fishing and some trout fishing. I've been doing it for years and it has several advantages over buying knotted leaders:
They are cheaper.
You have the ability to easily tweak formulas to your needs. For example, proportionally downsizing a particular formula to make a shorter version of a leader.
You become an absolute expert at tying the leader connection knot of your choice. For example, I can tie blood knots in my sleep, with one hand tied behind my back...drunk.
Once you get proficient, you can make them just about anywhere. I used to tie mine while watching TV or when camping or during overnights in hotels.
It's fun!
To get started I suggest you check out this website:
http://globalflyfisher.com/fish-better/leadercalc-2016
After that, you need the leader material of your choice (I’m not a fan of kits because I like different stuff for the butt versus the tippets and different brands for bass versus trout).
Other essentials are a small tape measure, a GOOD SHARP pair of nippers and I suggest investing in an inexpensive micrometer or dial caliper (available at Harbor Freight) or a “tippet gauge” that will allow you to accurately measure the leader material diameter because sometimes, the stated diameter is wrong.
Being off a thousandth or two can make a huge difference in taper and knot strength.
A small notebook (or your smart phone) to record formulas, variations, what works, etc. also helps.
Small adhesive labels to attach to the completed leader to record what it is and/or small Ziploc bags you can mark and store them in.
Unless you use finger cots or gloves, expect to get sore spots, maybe blisters and eventually callus on your fingers from drawing up lots of knots but after a while, you won’t notice it.
I definitely recommend wearing finger cots or gloves when making saltwater, bass leaders and the butt sections of trout leaders. The heavy mono or fluorocarbon can really hurt your fingers because of the extra pulling required to draw up the knots in the fatter & stiffer material.
Good luck!!