That building is being built to further nuclear research and to study medical isotope production here at McMaster. It is the result of a government grant. The proposed expansion of the Tandem Accelerator is also being financed by research grants, so everyone who wants new lecture halls can rest assured that none of their tuition is being diverted to these facilities that they will never use. Just for interest sake an article on the grant to Mac for the NRB expansion can be seen here:
http://www.ic.gc.ca/eic/site/ic1.nsf/eng/04695.html
Also, if anyone is curious as to where funding for projects happening on campus both currently and in the future comes from (and how much each costs), Mac does make this information available:
http://www.mcmaster.ca/mufa/ProjectSept15-10.pdf
On the topic of new lecture halls, those are to be included in the Wilson Building for Studies in Humanities and Social Sciences (Liberal Arts Building), which is also shown in the above document. Apparently Mac is also looking into an above ground parking structure.