The main reason why we don't recommend building a lease agreement through our platform is that forms cannot be served over SSL. Whenever you're taking highly personal information like banking info or SSN's, etc, it always needs to be done over a secure encrypted connection. Last thing you want is end user data leaking over the web in plain text. We want to move everything on the network over SSL, but there are some remaining complications out of our control when it comes to IDX data and how it's served from the providers. When those issues are resolved we will run everything, including gravity forms, over SSL.
The second reason is that platforms specializing in lease agreements will be much cheaper and offer more options. Custom building a gravity form is useful for many purposes, but rental applications we do not believe are one of them. You are far better served for your time and money with a company dedicated to lease applications.
That said, we do have some suggestions:
Decide on a 3rd party platform that has a great lease application product for you. Be sure that the lease application you have in mind can in fact be constructed how you intend on the service. A few options are RocketLawyer, Buildium, LawDepot, Cozy, or LeaseRunner.
Locate a freelancer to outline your lease application goals within your chosen software/company. https://www.upwork.com/. It's easy to post a job and take applicants, choose a freelancer to hire and keep you from spending your own time making the form.
Have our teams help you add it to your navigational menu, and consider various ways that call to action could be placed on pages, or sidebars of your website linking to the lease application.
Using this method you will save time involved, speed up completion, and save a ton of money while providing this valuable service to your end users.