Cardstock Jig

With a fine piece ofcardstock.

First, you adjust the line of roof and cut the piece of cardstock to fit by try an error

After you can draw on the piece of cardstock, when pushing it against the back,  the contours of the of the wall and the famous gorgeous detailled art deco column.

Next you use this piece of cardstock to drawn the futur back wall, in styrene or in a brick plastic pattern.

A few adjustement and you have you back wall cut to form.

Fill and sand

   I think you were on the right track. I'd probably glue the building together, then mask off the roof and fill the voids with fixall or other hardening putty. Scrape it off smooth as it sets up then sand it when fully dry. The back of these type parapets are usually covered with hot mopped tar and roofing paper or maybe tin flashing so I'd overlay the filler with something like that then weather the whole roof to match....DaveB 

I dunno...

I was up on the roof of a real building the other day, and it looked a lot like what yours already does. Not a lot of effort was made to give it any semblance of “finish” other that to make it weather tight.  Add some conduit and an RTU and call it good. 

What a great looking store, I agree......

this is a keeper.  To fill the void in the back of the vertical column I would use a thin sheet of plastic.  Scrape the paint off the edge so the glue will get a good surface.  Cut  the plastic slightly larger than the outside of the column and glue it on.  When it's dry use an Exacto knife #11 blade and trim it closer following up with a small file and you're done.

The front of this store will really come to life with some accent colors.  Take a #17 flat blade or a single edge razor blade and scrape the paint off the top of lettering until it is all white.  You might consider doing this to the tops of the horizontal ribbing also.  Too bad it says "PLASTICVILLE"  because that's what you're trying to get away from, right?

Take the #17 blade and shave off those letters.  If you can make this surface smooth all the better, but if not take a piece of white styrene and cut it to fit onto this area creating that flat surface you were going for.  Now get some decals or dry transfer letters and print the owner of the store's name vertically on this white surface.

If you spray the roof with some flat black or flat gray paint it will look a lot better because the plastic there now is just too shiney.  Don't forget to make some hand painted signs to put in the windows with today's specials.  Please show us more pictures as your build progresses.  This is going to be a cool building.

The plastic is soft enough to

shave the “plasticville” off, then smooth with fine sand paper. Paint window frames and trim over it stainless steel, to show off Art Deco look. I did on pharmacy kit.

 I

Putty

Like Dave B, I'd fill the back void with something, but I'd use lightweight spackle.  I've used it a lot as a sort of modelers putty and it works well, doesn't shrink, dries quickly and is easily sanded.  The prime and paint a grungy color, and, like Dave mentions, add lots of sloppy roofing tar around it.

Mike Horton - nice treatment on that building!  I think people often overlook the Plasticville buildings because they're, well, Plasticville.  They do have some great possibilities with a little work.

Al Carter, Mount Vernon, WA