According to Aristotle, moral qualities can be destroyed by both excess and deficiency. What example does he use?

I think Aristotle uses the example of food. Being happy in life is like being well fed. Too much food or too little food can cause us grief. Therefore our job in life is to find the correct balance or the ' the mean', not only when it comes to food but in all areas of life.

The mean is not the average; Aristotle, unlike Plato does not believe that there is an absolute standard of morality to which we all must adhere. What is regarded as good and efficient for one person may be too much or too little for another. Therefore, Aristotle is a relativist in this respect.

For Aristotle reason alone will not provide us with the correct way to live, it can only be achieved through a process of trial and error.

One example would be builders

Sorry, I don't understand your example of 'builders'. Could you please expand?