One of your criteria for a rental space here in Orange County may be that you can customize the space to fit your needs. More than likely, this will require some construction, and how this is addressed in your lease makes a difference. As a prospective commercial tenant, you have the right to negotiate the construction that takes place in the space you intend to rent.
Before taking any further action toward signing a lease, you can have your own construction experts assess the current condition of the space and otherwise inspect the site. You could also have him or her review the work the property owner intends to have done on the space. The results could help you determine what you need to discuss in reference to your lease.
Since you intend to have the space customized to your needs, you will not occupy the space for some time. Depending on how long the buildout will take, you may want to make sure you are not paying rent for a space you cannot yet use. In the majority of leases, your first rental payment would come as soon as you take possession of the space. However, you could negotiate your first payment as due when the buildout is complete. Again, consulting with your construction expert will help in figuring out when that should be.
Once all construction issues are resolved, you can then go back to the property owner to negotiate the buildout and first rental payment. Most property owners want a commercial tenant who intends to spend a significant amount of time in the space so they do not have to continuously search for one, which could mean leaving the space empty, and thus not profitable, for a period of time. Even so, they do not necessarily want to give you the access to the property rent free for a long time. An Orange County real estate lawyer with experience in the negotiation of commercial leases could help get you the terms you need.