They may have mandates that essentially require stick-built houses, which would be more expensive, and may make the lots financially unfeasible.That could be another reason why the lots were never built on.Lastly, consider that if it's a package deal, some of the lots may be buildable and some may not be (or may be more difficult, less profitable). 

My wife and I are on our 3rd homeowner occupied flip house and do the majority of the work ourselves.After 5 years of living in a construction zone, we too are starting to look to complete a cash-out refi on our current house in order to purchase our next house and a rental over the next 6 months.  

Find motivated sellers who will sell at a deep discount that will pay for any extended time that your offer considers or offer a small profit split with them.This idea may work out and I would like to hear more as you progress.  

It takes away from your profit potiential for an investment and as far as I know you can not debduct the cost in your taxes.

rentals that do not need major repairs- at least to start

There could also be non-profits that are looking into improving certain portions of the city as well. 

Those are just 'very, very rough guidelines', I'd say my last 3-5 flips average out to about $13-14 per sq ft - Kitchen, bathrooms, flooring, paint inside and out, one or two of the major systems (roof, windows, furnace, water heater), etc.  

My plan is to write up a contract which allows me to be put on the deed, rent the home out for several years and sell for profit at the end of the contract.

It's truly good for society, and I make a really nice profit that rolls into the new homes, while allowing the 12-25% cash on cash return to fund the things above.

@Darius Moezinia Refinance right after the completion of a 1031 is perfectly acceptable and is a frequently used strategy when cash is desired by the exchangor who does not want to create a taxable boot situation by taking cash or be seen as inappropriately accessing profit by a refinance immediately before a sale that begins a 1031.