Considering a shelter in the case of TEOTWAWKI?  There are many options.  I have posted many links from around the web below.  Whether you are just looking for a place to Get-Out-Of-Dodge if the SHTF, or you want a full  blown blast shelter, the options are numerous.  Hopefully these will get you started in your search for what will be right for your family.

Above Ground Shelters:
(Awesome, low cost shelter.  You will need to register for the forum to see the pictures.  Not a negative…I think preppers should be reading this forum anyway!)

Underground Shelters:
The Cellar – A simple, owner-built underground shelter (you may have to register for the forum to see the pictures)
The Cellar – a year later
20×32 Owner Built Cabin in Maine
Underground shelter constructed of buried school buses
Mini-underground blast shelter