If you received a quotation from a builder without a design done, you did not get a quote, You got an estimate!
What does your proposed renovation look like? How big is it? Does it fit? Is it compliant? How does your furniture fit? And much more.
To produce an accurate quotation that is honest and with a price that is not going to blow out, we need to add up every brick, length of timber, dirt to be dug our, labour etc and then, only then, we can give you a quote.