Can I set up ext warranty in checkout screen?

I want to set up an extended warranty option in the checkout cart based on percentage of final price, can this be done with attributes?

Not with attributes, as these are applied at the PRODUCT level, not at ORDER TOTAL.

SWGUY (Scott Wilson) may have some ideas and there is also a SHIPPING INSURANCE mod that is in the Free Add Ons that you may look at making a CLONE from...

Warrenty should be speficied on a product basis, since it applies for each product individually and may be different for different products. Just specify it as an attribute.

GOOD POINT tino !

I would absolutely agree here - and I am sure that anyone underwriting your extended warranty would want a watertight, legally-binding warranty agreement - specifying the product(s) covered in place too. This would include noting things like the product's serial number, date of purchase, what's covered and what's not, etc...

If you are underwriting your own extended warranties, please appreciate that these are regarded in law as contracts. I trust you are well aware of the need for clarity in such agreements.

I never BOUGHT an extended warranty as they are completely unnecesssary, but when I worked in Dixons (25 years ago) I sold a LOT of them - much to the delight of the store's manager. I always remember the customer having to append a signature to the agreement, indicating the contractual nature of the product.