I just put together a review with pictures here:
Putting together Green Grocer
This is specifically what you need to know:
* Blue arched brick (6005) for the awning is about 1 per piece but you only need 4. I got used ones for a lower price and to avoid making a separate order from the few sellers who had more.
* Dark gray door frames (30179) are very rare and you need 5, but the other version (60596) is functionally the same for a tenth of the cost. You also need one black and two white, and the latter can be found in Seaside House along with plenty of other window pieces youll need.
* There are plenty of dark green basic bricks which can be tricky to find but not extremely expensive.
* The decorations around the shop door (2431pb043) are from old Viking sets and most sellers only have a few. The prices range wildly, so plan your purchases well.
* The sand green bricks are a killer, since you need tons of them. You need 41 1×4:s and 50 1×8:s, which make up the bulk of the walls. You can either replace these with another colour (which sort of takes away from the Green Grocer) or you can bite the bullet. Since the 1×8:s cost more than 10 times as much, I went with 141 of the 1×4:s instead. There are slight problems with this: the 1×8:s normally overlap by four studs which makes a solid wall, but if you use 1×4:s they sometimes just stack on top of one another. This can be fixed by shifting some pieces around, but it ultimately looks pretty good anyway. Either way, finding sellers with these quantities isnt easy and now that the big sources of this part like Haunted House is out of production, it will probably get more expensive until they make it again. Incidentally, the Haunted House WILL cover most of your sand green needs if you use 1×2:s and 1×6:s to substitute for the 1×8:s, although that too is getting expensive.
* The sand green brick with a groove (4216) is kind of rare but not too expensive, and available from several European sellers.
* The white 2×2 panel (4864b) is rare but you only need two. To not have to make a special order, there are several variations that are functionally the same.
* The white 2×3 train window is very rare and those who have a few of these know how to charge for them. I went with light gray ones for now, although I might replace them down the line. Paying 2 per piece just stings, but they are rather prominent on the front of the building.
* The minifigs are wildly overpriced as sets since they mostly consist of standard pieces. If you break them down, you probably have most pieces already. I skipped them entirely.
* You want to get the kitten (6251px1), even though its a little expensive.