First off dont make it dependant on the size of the building, your new so flat fee $1500
Your going to need the Drone to take the Pictures , a license for the Dronelink software to get them, a mega fast computer to Render say 20 thousand pictures and a prayer it all turns out ok.
Once you get a few of these under your belt , move up to $3000 but this is because by than you will have gotten a faster computer , and. your turn arround time will also be faster.
Let them know your new to the 3D models an because of that your agreeable to any changes or extra needed , such as more scale if needed.
In the end comes down to Rendering and getting a good result , its not easy , seen many people fail at the end result or a result not usable for the clients needs.
One last note: Be sure to understand what the client is needing the 3D render for , as this can make or break your time spent on the project.
Dont skimp on the Software to take the picures , be sure to start with the best and than if need be work your way down the Software but only after you have sucess.
The Risk the company takes hiring you is that you stall the project , for there meeting and deadlines. With that said the learning curve is steep but the software has gotten more forgiving with the ability to Edit out the nonsense that sometimes show up on the 3d Render.
Phantomrain.org
Gear to fly in the Rain and get the job done.