The accomplishment of building investments is a long-lasting process resulting in considerable
financial outlays. Crucial decisions concerning construction solutions, technology of execution,
organization of construction works are taken at the stage of planning and programming. At that
time it is possible to predict the budget of an undertaking when it comes to preliminary cost
estimation. However, taking accidentality, uncertainty of results, appearance of factors that were
not planned earlier into account, it is important to know the total value of works. The solutions
adopted at the stage of planning are reflected in costs in life cycle and determine the kind and
range of possible risks. PERT approach used in the paper allows to present the costs of separate
stages of the whole undertaking in ranges along with the probability of appearance.