A new method is presented for the construction of ab initio quality approximate electronic charge distributions for large molecules from charge distributions of small molecular fragments. This method is reminiscent to building structures using Lego blocks. The electronic density distribution calculated using the method is quantitatively shown to be very similar to that calculated for entire molecules using conventional ab initio packages with standard basis sets such as 6-31G**, while requiring only a fraction of the computational time. The pre-calculated fuzzy electron distributions of base molecular fragments, stored in a data bank, are merged (rotated, translated, and subsequently added together) to calculate these approximate charge distributions for the molecule. The method requires only the Cartesian coordinates of the nuclei for the construction of molecular charge distributions. The speed of the method makes it potentially useful for molecular modeling applications where construction of electron densities of large molecules is especially important. The technique can be used to replace fused sphere models of large molecules with more realistic electron density contours. One additional advantage is that these contours can be displayed for a whole range of density values, from tight, high-density contours, representing the bonding pattern, to loose, low-density contours representing the peripheral shape and size features of molecules.