It was built approximately to scale, however is 1/2 the length and 1/3 the width of the Biblical dimensions. It was built to show the world how massive the Ark was and how so many animals could have been housed for a long time.
There have been several comments on the improbability of getting 2 of every animal onboard the Ark. Take a look at this website http://www.biblestudy.org/basicart/sizeark.html . Briefly... The Ark had the same capacity as more than 500 train boxcars. Remember, not all animals needed to be full grown, not every variation of every genus. Also remember that not every variant of every genus was required onboard as their variant species would be produced over the years. Also, check out http://www.answersingenesis.org/creation/v19/i2/animals.asp . Consider all the facts, the 1.5million cubic feet of space on the ark, 40,000 animals, and it makes a lot more sense than the little 4-animal arks you see in pictures and toys. This thing was massive and amazingly effective as a safe haven for thousands of plants and animals.
Also, for more information you can go to the ark's official website http://www.arkvannoach.com/language/en/ .
From: http://www.pbase.com/paulthedane/noahs_ark (Pictures)