We study the times to grow structures within the tile self-assembly model proposed by Winfree, and the possible shapes that can be achieved during the self-assembly. Our earlier work was confined to the growth of rectangular structures, in which the border tiles are prefabricated. By varying the relative rates between the border-tile and rule-tile attachment, one can engineer interesting new shapes, which have been observed in the laboratory. We show that the results from an extension of our earlier stochastic models agree remarkably closely with experimental results. This is an important further demonstration of the validity and usefulness of our stochastic models, which have also been used successfully in studies of error correction in DNA self assembly.