Upgrading vs Massing Income Buildings

Here you see how effective every upgrade is and if it might be more useful to build another one. The Chart below shows that upgrading a Market to Level 2 is better than building another. However its more efficient to build another than upgrading to Level 3. The Chart below shows that massing Sawmills Level 1 is better than upgrading. Once you build all you could, i recomment to upgrade one by another to Level 5.
 * Markets
 * Sawmills