Most models are based on paintings by seventeenth and eighteenth century artists. These usually show fat dodos with short legs. However, hardly any artists would have seen a real live Dodo and the paintings were probably based on crude taxidermy mounts. Since taxidermy as an art form was not well developed at this time it is unlikely that these mounts would be accurate (as with our Walrus).
Today, scientists working on Dodo bones have been able to develop a more accurate picture of what Dodos might have looked like. It seems that Dodos were probably much slimmer than this specimen and with longer legs.