With the exception of certain small projects tthat could be undertaken as permitted development, you will need the permission of your Local Authority Planning Department to develop. Whether it is a new home, extension to an existing home, new buildings within the curtilage of an existing building, change of use of buildings or land, and many other possibilities, your Local Authority Planning Department will want to know about it.
Development by householders is usually about extending and/or altering a home, normally their own, or possibly building a new structure, habitable or otherwise, within the curtilage of their home. The rules about Permitted Development within the Curtilage of a Dwellinghouse have been amended
two or three times since October 2008 to make it easier for householders to extend/alter their homes or build in their gardens without seeking planning permission. There is a good interactive guide available on the planning portal at the following link.
If you do need planning permission a planning drawing is about showing your Local Authority what you want to do. How big, where it is, what materials, what colour, and so on. But even if you do not require planning permission for your project others will need similar information. Your contractor needs information on what the project is to look like and how it is to be built so that he can offer you a quotation for the work.