Changing layout and adding custom forms for generated HTMLs

Hi,
Thanks for great product,

In Library management sample application, I could found any html or template files.
Sometimes it would be necessary to add or change forms or look and feel of data,
For example: lets say admin wants to see total price of reserved items from library for each user in list,
but reservation costs can change everyday,
which means data calculation should be dynamic and always should be calculated.
(example could be solved in different manner, but I need solution for custom HTML and forms)
where and how I can manage my custom HTMLs?

You can set field level permissions (Permission Level on fields and Permission Rules) to show / hide fields based on roles.

There are no layouts for forms, they are generated based on the field sequence.

See this for detailed explanation: https://erpnext.com/user-guide/setting-up/permissions/role-based-permissions

Dear rmehta,

The link you are providing delivers a 404 error.

This link is working:
https://frappe.github.io/erpnext/user/manual/en/setting-up/users-and-permissions/role-based-permissions.html