You mean something like Construct2 or Stencyl?
I'd suggest looking at those applications and breaking them down, almost like reverse engineering.
How does one pickup something with a mouse?
How does one snap it to grid?
How does one change from grid to freeform?
How does one reactivate an object that has been placed?
And so on and so forth.
I'm doing pretty much this for my game since everything is new to me and it helps a lot.
It is easier to manage tiny little scripts and then combine them rather than creating something gigantic - specially when you are not sure of the mechanics of it.
The best suggestion I can give though: Write what you want to do and start simple. Do little drawings in a notebook so you have a reference point. It is much faster to think on paper then with a computer.
By the way, there are quite a few examples and modules made by LÖVE users that might be helpful (map editors, particle editors, etc...) be sure to check the Projects section of the forums
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