The minimum size for a recognizable model of the Taj Mahal would be to scale of about 1:200. The complete main building of the mausoleum to this scale would require about one thousand rods:

Not much can be done to this scale, obviously. The model has to be overly simplified, and its internal proportions are unavoidably very inexact. In order to render, even if very roughly, the main features of the monument, and to approach its right proportions the minimum scale is of about 1:125. A complete model to that scale is shown in this page:

But the minimum scale to which the construction would not hide important details of the monument should be near to 1:50. To that scale the octagonal structure of the minor domes is noticeable, and the main dome can be built with a shape which really approaches the original, as shown in this page:

The following page shows a possible design for the minor domes, also to scale 1:50, and several views of the five domes at once:

In a previous version of this page I gave an estimate of ten thousand rods for building a complete model to this scale. But the main dome requires more than five thousand rods by itself, so probably between fifteen and twenty thousand rods would be needed, even if using an appropriate table or other auxiliary structure to raise the domes.