Counting empty lots in pro forma

[Sharee Mason]

I have a client trying to purchase a mobile home park.  It has a few empty spaces.  The seller has those spaces listed on the pro forma income/expense sheet as what they would bring in if they were occupied.  My question is, how do you value the vacant pieces?  It doesn't seem right to value them at the income they would bring in, because there's a lot of work involved in placing a mobile home and securing a tenant.  It's not like the lot will perform immediately, so I don't think it's correct to value it as if it would.  On the other hand, there is income potential there.  So should the vacant lots be counted in the purchase value, and if so, how?