I have built a GLR vertical boiler. Its been tested but not steamed. Its quite straight forward to build, i think i put it together in 3 heatings with a 1" burner. I did add some extra 1/4" x 40 bushes to give a bit more scope for adding extra's. Tubial Cane did a write up in model engineer which comes with the kit i bought, it was helpful when putting the boiler together.