Where is the property you’re looking at?

If you are seasoned or have a lot of capital, there are much bigger players you can look at.

Also might be good to talk with your agent and get an idea of what an extra storage space is valued at in your area (I've seen sheds be valued at several thousand before) so that might defray some of your building costs.

We couldn't afford it at today's construction prices.

Premiums are up at least around 20% in that timeframe. 

In a blue state I would probably eat the $600, but no way I would renew them at the end of their lease.

Anyone offering you US debt at 0% is a scam.Anyone offering you a yield of 50% is a scam.There are deals out there but you need to put in the work and find them.

If so, is that assuming that the builder builds at cost (and "proves" it by providing invoices/etc. by the subs)?

PM companies will pride themselves in finding a tenant quickly, often at the expense of top rental rates and quality tenants. 

Hi Emmanuel,Why don't you just use a 3 year prepayment at a 3,2,1 declining and take a lower rate?