Ok this might be some help https://imgur.com/a/LXbS3Z3

Nah no problem, just do send me a copy :P

Edit: I might actually be able to help with that. Gimme a moment.

Glad to help? Roman byzantines love arches and DOMES

This might help for visuals

Now with spiral staircases. Sorry about the last pic, I'm colorblind but it is highly likely you might suffer a little.

So this is gonna be weird to describe, but I'm gonna try. If it doesn't help maybe I'll make a post with pictures.

Here's how I do it. I pick a point where I want my dome to go. Then I decide how big I want the dome to be. Then from my point I pick 4 points (preferably evenly spaced ones) at the distance from point. Since every triangle is basically 1 unit away from a given point on isometric paper I highly suggest picking a point on the grid and making the points of the circle rest on the grid intersections too. I complete the circle by drawing curved lines between the points I marked originally. (Though you can do this with a compass I prefer to freehand. Cuz Lazy)

Decide how tall the Dome is going to be and draw a line upwards from the middle of the dome to the height you want (Not necessary but can help if it is big otherwise just put a little dot at the tip) then draw a curved line between the two deepest points that goes through the tip of the line you made to judge the height. That's basically it.

Edit: rereading this it is a little messy. I'll try a visual representation

Glad it was of use. Good luck to thee

I can see that. It's the domes I think. Domes? DOMES

Oh now that you mention it! That's a good point. I can't believe I forgot about that one.