If you're planning on creating a big painting, it's definitely more cost-effective to build one yourself. For me, a large painting is anything with a side that is 3ft.+. This video is not meant to be a step-by-step tutorial, but an overview to show how I build and stretch my canvases. If you have any questions or want clarification - ask away in the comment section!
Disclaimer: I'm not a professional, but this is how I build my canvases and is what works for me :)