She was addressing a conference of the SA Institute for Civil Engineers (Saice) in Ekurhuleni.
"There is no need to loot," she said. "No one should lose for you to profit."
The Public Protector said the majority of business people, like their counterparts in government, were people of integrity, who had the country's best interests at heart.
However, there are a few bad apples on either side whom she implored to strive to give value in order to be rewarded accordingly.
She mentioned her investigations of maladministration against the Nala municipality in the Free State and the City of Johannesburg in respect of service delivery issues at Braamfischerville.
She related examples from these investigations of unscrupulous engineers, who were dishonest in their trade, leading to faulty sewerage systems that posed health hazards for local communities.
She also referred to her experiences and observations during a systemic investigation into problems plaguing government's RDP housing programme.
Some contractors were paid for shoddy workmanship and work not done, while others inflated costs.
Misconduct by inspectors
Other problems included the conduct of inspectors who certified unfinished projects or those that were done not according to specifications, leading to the payment in full of the contractors involved.
The Public Protector also cited a case dealt with by the Competition Commission, where established construction companies were found to have colluded to get government contracts.
She said the built industry had a critical role to play in giving effect to the constitutional promise of an improved quality of life for South Africans.
This is in view of government's planned investment of R847bn over the next three years and R1trn already spent in the last five years on infrastructure development.
This included ensuring access to quality healthcare, education, water, sanitation and housing through the construction of public hospitals, schools, dams and RDP houses, among other things.
She commended Saice for its code of ethics, which calls on members to, among other things, act with integrity and fairness, have regard for the public interest, avoid conflict of interest, treat people with integrity and not to misrepresent their areas of experience.
"If all engineers in the country, even those who are not your members, operated according to this code, we would not have come across the things we often come across in our investigations," she said.