Estimating Rent Per SQFT On Building w/ Open Lot In Back

[Bryce Kammerzell]

Hey everybody! 

I'm having a hard time finding really good info on this while searching the forums. The deal I am buying is a commercial property. It is a large steel shop with two offices, meaning two businesses could operate out of it. In the back is a shared lot, a little over 21,000 sqft in size. It is fenced in and secure. I ran some comps and believe the building itself can rent for $8 to $10 per sqft now and $12 to $15 per sqft after some renovation. The part I am having problems with is the lot.... how much can the open lot (which is really just fenced in storage) rent for?  If a business wants to rent part of the building and needs the lot, would you charge them the same dollar amount per sqft as the building? I imagine it would be less... but how much? 

Any advice is appreciated! Thank you!