Build a multi account management and billing software with GST for India

I want to build one accounting software which is able to manage multiple companies accounts at once as well as it is also able to print sales bills and all other necessary accounting documents for INDIA including GST and income tax and all other things. I have figured out that what I need is similar to the software SPEED PLUS 8.0 (GST) from [login to view URL] The software is desktop based and is able to work in network also. It must be developed in .Net Framework using c# and backend as SQL server or MS ACCESS. Developer has to handover all original source code to me.