Harvard Library has digitized their microfilmed collection of HH Richardson drawings. There are sketches, plans, lots of stuff. Emphasis on LOTS - look down the page a bit for the 21 Microfilm Reels.
https://hollis.harvard.edu/primo-explore/fulldisplay?context=L&vid=HVD2&search_scope=everything&tab=everything&lang=en_US&docid=01HVD_ALMA211817496640003941
You will want to spend some time on these, I think!
https://hollis.harvard.edu/primo-explore/fulldisplay?context=L&vid=HVD2&search_scope=everything&tab=everything&lang=en_US&docid=01HVD_ALMA211817496640003941
You will want to spend some time on these, I think!