First of all, why have multi-tile objects when you can duplicate things so easily in the editor? I understand it's important for bigger objects, but a simple floor or wall? No need to have it take up two tiles - with the right texture it can look as well if it's just one tile.

Next part, wall corners. Here I had to watch two times that part of the tutorial because I just couldn't believe how stupid the idea was. I mean, you have to build a corner from two different pieces? WTF??? Her's what I mean. In normal engine, you'd only have two tiles: a wall tile and a corner tile, like that (imagine green as transparent and the frame is there so you can tell the tiles apart:

https://i.imgur.com/dWIWHz6.png

Going top-down for this, but it's also applicable to iso engines. By rotation, you can get other directions for either and build even a complex room with these (again, grid provided for easier discerning of separate tiles):
https://i.imgur.com/iaAmq82.png

That's really all you need. But of course not in Shadowrun, no here they had to make such confusing way to build corners for seemingly no reason. No wonders I had problems with making a simple square room without looking at tutorials!

And who had the bright idea of having me to keep running an instance of the main game while editor is running, instead of starting up the engine when it's time for testing anyway???

Mind you, that I'm not speaking from the place of ignorance either. I've been programming since I was 10, making games since I was 14. I've used all sort of engines and game making software. Clickteam, RPG Maker, Game Maker, GDevelop, Unity, Unreal. In fact I'm working on my first commercial project, which is a 3D platformer and has extensive modding tools.

In fact, the same editor I use for making levels in main campaign will be shipped to the players, without any sort of dumbing down and introducing any limits (I plan a few ways to let players profile a level, but no limit on how much memory/gpu a level can use).

And I simply couldn't live with myself if I had to explain how to make a friggin corner!