Hi Killacam94,
Thanks for your post and welcome to the forums. It's great having you on board with us in the Community.
Unless the outbuilding has it's own address, it's likely the engineer will need to install in the address we have on file however saying that, the engineer may be able to run the cable. Usually, there will be a pre-install visit to ensure the cable is fitted ready for install. Speak through your options with the engineer then and if you are unhappy and wish to change things, we can arrange this.
Keep us posted on how things go.
Thanks,