Garage Extension

Hi, I?m intending to extend my current garage that has a flat roof to one with a pitched roof. My intention is to build a double skin block wall (to keep the cost down) at my boundary approximately 10ft high and fix joists from the main house to the new boundary wall. First question is is how deep do my footings need to be ??? I?ve read varying opinions like 1m down, until I hit solid ground or could I dig down to my kitchen extension (single storey) footing and follow that ???? Would I need to tie the new boundary wall into the existing kitchen extension wall ???? The span of the new joists will be approximately 4500mm, is this too long and what would I need to do if it is ??? Do you also recommend the fixings that do NOT require any kind of wall plug. I?ve seen the bolts that fix straight into the pre-drilled hole, would they be sufficiently strong enough to hold the wall plate and the additional weight of joist and tiles I?ll be using. With regard to the block work would you also recommend getting a decent brickie in to do it ???? Due to financial constraints I was thinking of doing it myself and although I?m not a ?seasoned pro? I?ve done a few garden walls etc. Apologies for such a long post but needs must I'm afraid. Thanks for any help in advance

Sounds like a general read-through of building regs part A might be in order, and a chat with planning dept?