Extension on house

Has anyone done an extension on their house? I know taxes increase obviously and the costs of permits etc. but for the actually work, how much have you paid for an extension? I would like to add on 2 12x12 rooms. House is a ranch style. Anyone under take a project like this and has feedback?

Re: Extension on house

We are looking to put an extension on that would roughly be 12' x 20'. Note that it includes a kitchen so the numbers are higher but we were up around $90K in estimates.