I have a web-form on my site with several questions, which allow to the costumer to design his own product. Every question have several types of answers and final price of product depend on the choices. So, it is impossible to predefine the price of product before the submission of the form.
How to calculate the bill in compliance of the form data submission and then proceed it to PayPal?
Is it possible to solve by Formassembly tools or I need to develop third party script?
You should be able to make it work with FormAssembly.
I would recommend you first build the form with a free account. You will need to use a combination of calculations and conditional fields to make it work (check out the advanced tabs for each field). Once you have computed total (or unit price), you can upgrade your account to the professional plan to use the PayPal connector.