You must have a basic plan on the type of home you want and how many containers you will need before you buy the containers. You will find containers coming in different standard sizes. Few of them are suitable for living rooms and bedrooms. You can convert the smaller one to kitchens and bathrooms. So buying the required number and size of containers becomes easy once you have basic prefab shipping container villa design ready.
Please read the originial post here: http://www.starhouse.com.cn/details/prefab-shipping-container-villa