What makes you say that it's a DIY job? The white paint is not original. It's a really thick and poorly done powdercoat. Other than the paint, the frame looks like it was built well enough. Once the paint is off, then I'll be able to see how well/clean the brazing was done.
Plus, the pantographing really makes me think this was done by at least an established builder,(probably a small local builder) with their own brand.