In many countries, teachers often have to set their own questions for tests and examinations: some of them even set their own questions for assignments for students. These teachers do not usually select questions from textbooks used by the students because the latter would have seen the questions. If the teachers take the questions from other sources such as assessment books not used by the school students, this will constitute as plagiarism. Although they can refer to these other sources, they still have to modify the questions. It is during modilcation or setting their own questions that teachers may encounter problems which they may not be even aware of. The main issue is that students may get different answers if they use different methods to solve such problems. This article describes a general method called theoretical or mental construction, which teachers or writers can use to check whether a given geometric figure, or one that they have designed, is mathematically consistent. In addition, for some examples, the author has also discussed how to find the correct value without constructing the actual figure, or how to adjust the values to more suitable ones, such as whole numbers.