Had fun building, all the pixel art is really nice and so is the concept.
I guess my feedback would be just quality of life stuff that is most likely planned for later. Stuff like having the different objects found in different catagories, some tool tips on each item that say what they are would be nice when you hover the mouse over, since some of them I couldn't really tell what they are.
-Scrolling through items is a bit sticky/not really smooth when using the scroll wheel.
-I hope you add a fullscreen feature, since I use a 1440p monitor everything was extremely tiny, had to change my desktop resolution to see everything.
-Would be nice if tiles could overide each other, I was placing down tiles then later changing what I wanted where I had to delete them first to place a new one.
-Maybe a middlemouse click, hold and drag would be a nice way to navigate instead of the arrow keys.
-Maybe right click would be handy to quickly delete objects instead of switching modes
So yeah, not really criticism, more just things to think about I guess, I really look forward to how this keeps developing!