Think of installation not construction. Sunrooms are designed and manufactured to your individual specifications and installed at your home. Installation can often take less than two weeks and causes minimal disruption (debris, dust, etc.). Permitting and design fees are less costly. Best of all, a sunroom wont require substantial modifications to your home.
The answer depends on the glass used in the sunroom. There are a variety of different glazing options used by each sunroom manufacturer, such as single or dual pane glass. Each option allows more or less heat into the room, measured as Relative Heat Gain.
The glass with the lowest Relative Heat Gain (39) is called CONSERVAGLASS PLUS. Its only available on sunrooms manufactured by Four Seasons Sunrooms. CONSERVAGLASS PLUS blocks 85% of the sun's heat, helping you significantly reduce cooling costs.