Hi, thank you for your feedback, yes, we will include a shadow or at least an indicator where you can see if a tower can be placed there when you release the mouse button. The green number left to a tower icon is the purchase price and the right, red price is the money you get back when you grab a tower from the playfield and sell it over the trashcan in the lower left corner. The tutorial and better UI will improve that in the next version. Already working on it :-)