Before renovating your home it is necessary to estimate the amount of remodeling it. This wills aloe you to decide that whether you want to renovate your whole house of few parts of it.
Various types of loans are also available now days for renovations which can solve all your problems of costs. Actually estimation is not possible while building your new home or even going to have renovation.
Cost will also depend on your choice of renovation. But if you are thinking about a structural change like roof extension than it will be more costly compare with normal renovation.