Download and install Google Earth Pro, it's free!
Go to where you want to plop the building. Hit "R" to center yourself above the plot looking straight down. Make sure Terrain is unchecked. Click on the polygon tool. Here I shall add a tower to World Showcase Plaza...
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Left click to drop corners and edges of your polygon. Right click erases a point. You can grab and drag points around. You can chose the color of the line and the fill and their opacity. If you don't want a fill, but just a wire frame, reduce area's opacity to zero. Likewise, zero opacity on the lines hides the frame. Here's a pentagon...
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When you got the right shape and placement click OK to save it. Now, we'll add height. Right click on your polygon on the map or on the places menu and click Properties to alter it. Go to Altitude. Chose relative to the ground and check Extend sides to ground. Use the slider to add height or type in the altitude (in meters). Let's make it 20m tall and click OK....
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Now you want to go into 3D mode, so, click Terrain and 3D buildings. Now, position yourself (the camera's POV) to see how the model looks in 'the real world.'....
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