The calculation of equivalent collection areas is important for the lightning risk management of structures. Three problems are frequently encountered in practice: (1) how to calculate equivalent collection areas of complex shaped structures? (2) how to distinguish clearly between isolated and non isolated structures? (3) how to calculate equivalent collection areas of non isolated structures? The solutions to these problems are given: (1) through software modeling of structures; (2) if the equivalent collection areas of two structures overlaps, they are considered as non isolated structures, and otherwise isolated structures; (3) a new method is present to solve this problem. An example of several buildings is given to show the advantages of this new method.