A free mod for Stardew Valley, by Esca-MMC.
Farm buildings, such as houses and schools, can be built on any tile in the game, including the water tile, which is usually the lowest one in the row. In this way, you can place buildings on otherwise non-valid tiles, such as water and other obstructions.
The Build On Any Tile mod allows you to do this by simply downloading it from the Files tab in the game.
After downloading it, you can find the file in the Mods folder in your game directory, or the Downloads folder, depending on your device.
The mod also includes options to enable or disable building placement on certain terrain types and obstructions.
The mod supports both spacechase0's GMCM and the standard menu, so you can change its settings from the main menu.