Do I have to create proposal for description of work in my contract ?

You can do whatever you like :^)

However, if you want to be sure your contract is valid according to the laws where you work you certainly should find a local lawyer who can help you.

In general it is less expensive if you draft something and present it for review. The alternative -- you find a someone who knows enough about your type of business to understand its ins and outs, or you sit down with the lawyer to explain in detail--can be pricey, time consuming or both.