You'll be fine with this - it is an easy house! Make design pattern for size and cutting and everything will work out beautifully. Have you done RI piping yet? If so, that is the way I'd go for the trellis, otherwise you will need to use gumpaste and let it dry. If you use a pattern you can premake your roof joining it with RI and let it dry otherwise you will need to carve your cake appropriately and you will have to be sure about the measurements.
Good luck and remember to post your picture!
No I have no idea about RI. Thank you for the pointers.. I hope it goes really well. I will post pics!