That's so impressive!

How do you make the arches look so good? I took one course of 3d drawing similar to this last year. The course included drawing a house's blueprint, two outside pictures from two different perspectives and 3d picture inside one of the rooms with furniture and shit. That's much more simple than what you showed us here, but I was having so much struggle with all the furniture that had round parts in them lol

Drawing the arches (curves/circles in general) is pretty easy. Most people get away with an "aproximate angle" by using a french curve (the tool with lots of curves on it), but you have to bear in mind that in axonometric and isometric drawings there is ALWAYS a way to draw anything, but it can get quite tricky depends on the curve or intersection you want to get. If you want to be methodical you have to learn a LOT of formulas and techniques to draw everything 100% exact.

Back to the point, those arches are fairly straight forward, draw the square, draw the middle lines draw diagonals from middle to the corners and you will get specific points from which you use the compass to get the exact curve.

Edit: Here's an example of where it gets tricky

when you get intersection curves and you need to use those tables in the corner to create "generator points" (or.. generators) to create each point of intersection. So much fun explaining this haha