I still have the first frame that I ever built. It now has over 80K miles on it and still goes well, but as stated by pondlife, you will always remember your errors. All of my frames were built over thirty years ago before the internet and all the how-to videos and descriptions. They were built free-hand, i.e. without jig or other fixtures, using little more than a vise, files, hack saw and oxy-acetylene torch. To align the frame, I used the grout line in a tile floor. After about 10 years of use, I finally got around to checking the alignment and it was spot on (how is that for luck?).
I can't begin to count the number of people who I know who have a half finished frame building project in their cellar/garage/storage locker/closet... If you can't afford to buy a custom frame from one of the less expensive builders, you would need to either have plenty of available time that you do not value too highly or you are likely better off to not start with the building. To better understand this, calculate the cost of the framebuilding items that you would need from Ceeway and subtract that amount from what you would pay for a custom frame (they start from about £500 on up from experienced builders using suitable butted chro-moly tubing). Then realize that it is virtually assured that a first-time builder working alone will make at least one noteworthy error during building and you quickly end up with a considerable outlay of money without any benefit. (you can see one of my errors in the photo of the BB of my first bike here below. I rippled the chainstay when I went to set the rear triangle. To prevent any subsequent nasty cracking of the stay, I thought it best to reinforce the area with a fork tang)