Tell bidders about the change, not just the building
There is a temptation to quote the current state and deal with the change later, on the basis that it keeps the comparison simple. It does the opposite. A provider who does not know an area is about to double will build a roster and a resourcing plan around the wrong size, and the adjustment then arrives as a renegotiation rather than as a planned step you both anticipated.
Share what you know, including the uncertainty. Saying that a mezzanine will probably be fitted out in the second half of the year is more useful than saying nothing, even though the date may move. Providers deal with this regularly and a good one will price the known scope and describe the mechanism for the rest rather than refusing to engage until the plans are final.
