Who pays for changes needed to the layout, new walls, and electrical work in a leased space?

In a lease situation, it is typically the landlord who pays that and that is agreed upon in the lease upfront. What you try to do is get an understanding in writing, a schedule on the back of a lease that says what following tenant improvements will be performed by landlord at their sole cost. Usually those renovation costs are born by the landlord and are incorporated into the eventual lease and lease rate.