Walls and such are 500 gold per item placed ... haven't seen (or don't recall) the design you want to use, but if you can do some rough tallies of pieces, then you can get an approximate cost.
Roofs are not the easiest to manage but I prefer them myself. I've also found that of all the roofing choices only a few look and work well in the CC (no gaps, offsets, etc). However some folks like to use open roofs for plant growing, rooftop gardens, etc.
My current 18x18 on LA/Malas is about 500K cost because I have an open area in the center that goes all the way up. My former design was closer to 620K, had lots of roofing, little open area.