The valuable city planner from foemanager.com was previously a great way to design and build your city, but it is no longer available due to an unfortunate choice by the Forge of Empires game developers.
Reconstruction mode (unlocked in the technology tree in Early Middle Ages) offers some similar features and is currently the most convenient way to design a city. Some shortcomings include:
Only buildings you currently have placed in your city can be arranged
Every building and road must be placed back in your town before the design can be implemented
The city planner tool can no longer import cities, but it was very loved by the community and useful for:
Adding new buildings and removing unwanted buildings
Adding and removing roads
Keeping track of available population, happiness, supply, and coin production