How can i get the custom category attribute value and that value should be count in product total price at the time of place order ?
I'm sorry this doesn't exactly answer your question, but hopefully it will answer what has been asked:
A custom category attribute doesn't exactly make sense on any page that is not a category page or reference a category object. If you are attempting to get a custom category attribute from cart products, then I could probably understand but what happens if you have a product in multiple categories?
Perhaps what you mean is a custom product attribute, but even so, appending an ambiguous price amount at the time of placing an order is a rather sneaky and deceptive move. Perhaps I am misinterpreting your question, but if not, then I think you should consider displaying whatever additional amount you plan to append to the product total price well-before the time of placing the order.
Be sure the customer is fully aware of the total amount that could be charged to their payment method on the checkout/cart page, but definitely ensure they have their absolute final total amount on the checkout/onepage under the order review section.
Appending additional amounts to the totals most likely would require for you to create a custom module with some special classes extended for the totals collection. It can be a little tedious to do, but perhaps following classy llama's blog post: http://www.classyllama.com/blog/unravelling-magentos-collecttotals-core-process would help.