Commercial store: Dividing one space into 2 separate stores

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Hello everyone. I'm new to BiggerPockets and managing commercial property. I'm seeking advice from members who have any experience in this matter.

I have a a tenant whose lease is expiring soon. He's up for a renewal. He wants to downsize his space and rent the half of the space. If he is not allowed to downsize his rental space, he wants to move out. 

I'd need to put up a new wall and do some interior renovations. For a commercial property, which side, landlord or tenant, usually pays for this kind of project? Nothing is stated about this in the lease. I know that it's up for negotiation, but I wanted to know the usual practice for commercial properties.

Your advice would be greatly appreciated. Thank you!