Read this terrific article - Want to buy some air? Some cities have plenty to sell - to appease your interest in air rights and development.
a) Developing a deck (the platform in the air where development happens) to build upon is quite expensive; &
b) Financing is limited as there are minimal real property rights associated with air rights, which can be foreclosed upon (collateral).
Based upon the expense and lack of collateral, perhaps development for air rights is ripe for crowdfunding to get the job done. In crowdfunding, accredited investors (net worth of more than $1 million or have earned $200,000 in each of the previous 2 years) can provide the requisite funding in consideration of equity stakes in the development company, to get the project funded, built, and ready for tenants.