How new are you to this? Familiar with working on bikes? Have many of the parts laying around already that you want to put on it?
New frames might seem like a cheap way to go, but if you have to buy all the pieces parts to put on the frame then you'll likely be more than what you could have purchased an already built bike. As well, some of the tools you need will add to the cost and some may only be used for that particular part you are installing and may not be ever used again.
If you are building the bike because you want specific things on it that you can't get on model sold fully built and are okay paying more, then building your own is realistic and will be educational.