A basic method for assessing investment projects is to determine their profitability
with the use of Net Present Value and Internal Rate of Return. These methods take into
account time value of money, which enables to spot the changes in the whole
investment process. An investor comparing different variants of a planned investment
should consider expenses incurred also during the use of a building. Considering all
costs in the whole life cycle we take into account a long time horizon. Therefore,
predictability is encumbered with errors stemming from the possibility of occurrence of
random factors which are considered in the model to be risk factors causing a change of
a certain group of costs (standard deviation from an expected cost value). The rise of
costs is unfavourable to an investor. Therefore, it seems appropriate to include at the
stage of planning an investment all costs in the analysis as well as to assess their
probable deviations considering risk factors. For this reason PERT approach was used
in this paper, emphasizing possible changes of NPV value. It influences indirectly a
determination of potential reserves considering situations that are hard to predict during
investment realization and exploitation