You are asking very basic questions that suggests an experience level that is not going to result in an efficient use of your time, or those on this forum. Basic engineering: determine the loads, discover the soil bearing capacity and characteristics, design the foundation. API 650 slope is 1 inch in 120 inches cone up but many others are used with great success, depending on many many factors. Insulation depends on the thermal properties of the stored product and the foundation as well as the acceptable operating temperature range. There is lots more to know and learn, It's going to be tough for you to do that in this medium. Good luck!