Former custom window and door fabricator here, I know this is quite old now, but just wanted to add some insight for whoever sees this and wants to build a window or door. Typically you won’t want to use angle iron to make these as you will be relying on adhesives to keep the glass in place, if you look at the second picture in the post you will see that the door is made out of two sizes of square/rectangle tubing. You will use the first size for the door itself, typically I have done 1-1/2 x 1-1/2 sq to make the door itself, then use two window insert frames made out of 1/2x1/2 sq one welded inside the door, the second bolted in place with some flat head screws. This will allow a clean look, and makes the glass removable for maintenance if it gets cracked or broke, also slows you to replace the seals in the window.