Rome was not built in a day is an idiom that is used when one wants to express the fact that something should be done properly and not in a rush by ignoring details. It refers to the fact that any city, not just Rome, cannot be set up in a single day as it requires meticulous planning.
1. Setting up all the facilities for the Commonwealth Games would obviously take time. After all, Rome was not built in a day!
2. The football coach was aghast at the Sports Ministry's high expectations of getting together a team in time for the competition. The coach bluntly told them, "Rome was not built in a day – I need adequate time to select and train them".
3. Getting an idea for a new product was one thing; launching it strategically in the market was another thing altogether as Rome was not built in a day.