I'm still pretty new myself, but I've found the best thing to do is look at the windows. If it's a house you can go into, the windows will be actual see-through windows. If it's just an asthetic building, the window is just a bmp on the side of the house. Lots, LOTS of yellow dots on the map are this structure right here: The loot is under the slanted roof. A lot of the blue dots are an outhouse sized building: They're often tacked onto the back side of an unenterable house.