I'm on pc but I guess building houses remain building houses. If I may relay some ideas picked up from other forum members along with my own, here goes:
First build, avoid complications like multi-storey houses. If yo want a guide to sizes, I'd personally say one block on the grid is equal to about 3 ft. So draw up a rough plan of what you want on paper. Mark your sketch in units of "number of blocks". That will avoid a lot of complications. Then make sure in your sketch you have provided for both current and future inhabitants, like spouse and kids. Once you have your walls drawn (in the game) you should automatically have a roof, which is fine as is for a first build. Then paint your outside walls. Next add exterior doors and windows. By this time you should be ready to just go on creating instead of being all planned out. Make hallways at least 2 blocks wide to avoid "traffic jams". Design your interior from the foyer through to the end of the hallway. It makes "keeping in touch with reality" a bit easier if you imagine touring a new house as you go along. So... Enjoy and good luck! And welcome to the forum.