"Rachel" wrote in message
Are there any laws stopping me from blocking off an external door? If
not, is this an expensive job? I have absolutely no idea how to do this
and would have to pay a specialist to do both these jobs.

Building and fire codes require certain means of egress. If you put in
French door in another place, you most likely satisfy the code.

Next, what do you meat by "blocking off"? If it will be completely covered
inside and outside, no one will even know it is no longer an entry. Cost
will vary depending on materials needed, siding, sheetrock, etc. few
hundred at least, I'd guess.