Yeah, the graphics were placeholders that I made in a matter of minutes or sometimes even seconds. Didn't have time to make anything look good and I'm not really an artist anyway. Glad you liked the game! It was a lot of fun to make. I might consider expanding it in the future.
As for the inventory system: I gave each item a list with coordinates of the tiles it was taking up (starting from the top left corner and then I just had the inventory iterate through that list to check if those places are free. But that's probably a super bad solution. I'm certain there are much better ways to code it. Probably better to save the shape of the objects in a grid too lol.