Michelangelo was either unable or unwilling--probably unable--to furnish the necessary plans and drawings.

In the eighth chapter of this book I have discussed the hesitations with regard to the interior of the sacristy which are revealed by some of his extant designs for it.

We also know that he was not in the habit of preparing accurate working cartoons for the whole of a large scheme, but that he proceeded from point to point, trusting to slight sketches and personal supervision of the work.
Thus, when Vasari wrote to him from Rome about the staircase of the library, he expressed a perfect readiness to help, but could only remember its construction in a kind of dream.

We may safely assume, then, that he had not sufficient material to communicate; plans definite enough in general scope and detailed incident to give a true conception of his whole idea were lacking.
VIII Passing to aesthetical considerations, I am forced to resume here what I published many years ago about the Sacristy of S.Lorenzo, as it now exists.

Repeated visits to that shrine have only renewed former impressions, which will not bear to be reproduced in other language, and would lose some of their freshness by the stylistic effort.