You get a selection from three random "buildings" at the bottom. When making a selection (hover first to see details) you will se most have a gold coin icon. This is how much gold you get when placing it. On top of that, when hovering it will tell you how much +gold you get for adjacent tiles. It take a little getting used to but once you figure out what the buildings are by their icon you can start doing some cool stacking to really make bank and pay the tax to continue. If you see a monument at the bottom it is almost always best to play that especially early game as they are worth 15 gold (just don't place them too close together)
Hope that helps!