Training puppy to use his own "restroom"?

Have anyone tried this before?

I used to have a cat that goes to her own restroom (located outside of
the house, a big dog house with a litter box) through a pet door in the
laundry room. I've recently gotten a Maltese puppy and seriously
considering training him to do the same thing.

So far, I've been putting housetraining pads just right in front of the
pet door and he knows to pee on the pad some of the time (when he's
confined in that room). I've shown him the door to his restroom but
he's not very interested in going through.

Paula...

Cats are born taking to a litter box. Dogs are not born taking to any
particular type of pee area, though they often like more absorbent
materials, which can be a problem when you have carpeting. Dogs learn
where to go potty by you training them.

If you want your dog to go out the pet door to go, show him how to go
in and out by lifting the flap for him and giving him a treat when he
goes through it. The flaps can be scary, so helping him out this way
makes it easier. As he gets the hang of that, you can move to letting
him do the flap on his own knowing that you are waiting with a treat
on the other side. When he needs to go, take him out to the area
where you want him to go and tell him to "go potty" or whatever you
want to call it. When he does, praise and treat lavishly. Don't just
leave him anywhere in the house with a pee pad or he will get
conflicting signals. Watch him for any signs that he is looking for a
spot and scoop him up instead of letting him go ahead. Take him
directly to the spot where you want him to go and tell him to go and
praise and treat when he does. Once he knows where he's supposed to
go and how to open the pet door, start putting him through the pet
door and telling him to go potty, or whatever command you taught him,
and he should go do his thing. After you've done that for a while, he
should be able to do it himself consistently while you watch (instead
of looking for a spot where he happens to be, you should see him head
for the pet door when he needs to go and look for a spot out there).
If he has accidents, go back to watching him all the time and making
sure he goes outside and gets rewarded for that and interrupted and
redirected for anything else.

Any opinion is welcome.