To build hotels in Monopoly, you must first acquire four houses on all properties within a color set, effectively owning the complete set, and only then can you exchange the four houses for a hotel on one property. Motels aren't an official part of Monopoly, but players sometimes use "motel" as a playful term for houses; always ensure building adheres to the game's house rules. Strategically, investing in developing full color sets, especially those adjacent to each other, can create formidable rent incomes, placing significant financial pressure on opponents.