Construction works need to be implemented in accordance with design documentation, technical and performance specifications as well as being carried out safely, on time and within budget. There are however various events, which can occur during the process of implementation, some as a consequence of the natural environment, others occupational, which can either disrupt the execution of and/or have a negative effect on the result of works. In such situations, the duration of works may be prolonged and thus the costs of a particular task may increase beyond the planned budget. A series of such events may lead to the final deadline and the total cost of works completion being greater than that which had been fixed in the contract. However, assuming the parameters of the PERT-beta probability distribution and three-point estimation method, it is possible to estimate and thus plan for two kinds of risks to works. The first is the risk to the deadline of works, and the second is the risk to the cost of works. Changes in risks are presented using charts of risks. These charts describe possible changes in the interval of risks [0, 1] depending on a series of increasing values of deadlines and costs affecting works completion.