Does anybody think that the Ipad would be useful (able to/apps available etc) for designing a home (self build)?

Does anybody think that the Ipad would be useful (able to/apps available etc) for designing a home ?

Are any good apps available (UK, France?)

Which would be the better version? I presume the Ipad 4 because of the larger size/screen quality but I do like the Mini!

I am also unsure of the capacity to choose (I a person that always thinks bigger is better as memory cannot be added), and also if I should have the 4G option, which would come in quite useful on the building site but I already have an I phone and don't really want to pay a second bill?

Thanks