Check out the zoning regulations in your area to see if you need to apply for a zoning change. If your barn/home is not zoned properly, you will not be able to get the permits and certificate of occupancy you need to hook up utilities and sell it later on.
Look into the cost and feasibility of hooking up the necessary utilities to your barn/home. Most barns are equipped with electricity and running water, at best.
Hire a foundation expert look over the foundation of the home to see if it is structurally sound and can support all the weight that would be added to it for the conversion. An inspector or structural engineer needs to look over the structure itself to ensure that the building materials and existing framework are adequate for the job.
Have a pest control expert and an environmental consultant look over the structure to address any chemical or biological hazards, or pest infestation issues. If there are any endangered animals or habitats, like nesting bats, you may need to involve a wildlife expert in removal of the animals to a safe habitat.
Consult with an architect about your ideas on how to use the structure. Load-bearing walls and additional structural support may be necessary. Think about how you live, your needs and the purpose for the various rooms in your home to help the architect with the design.
Take a good solid look at the "bones" of the structure with an eye to what you have. The most effective and least expensive conversions are the ones that make the most of the space as it exists and use materials already present in the structure.
Pick plans, designs, materials and colors that work with the natural character of your new home.
Plan to go over budget, so make sure you have a source of extra cash. Renovation loans can be tricky to get, and some pay vendors only on a schedule, so have cash on hand to take care of small and short-term expenses.