1. Place 2 tablespoons chocolate chips in each sandwich bag; do not seal. Place all bags together on microwavable plate and heat on MEDIUM (70%) 1-1/2 minutes. Rearrange bags on plate and microwave 1 minute more or until just melted. (Knead bags, if necessary to allow chips to melt completely.) Squeeze melted chocolate to one corner of each sandwich bag and seal bags. Snip off a very small tip at the corner.
2. Count out 20 unbroken pretzels, 1 bag of melted chocolate and 1 sheet of foil for each cabin.
3. For roof, place 8 pretzels side by side on a sheet of foil; squeeze a small amount of chocolate between pretzels to hold them together.
4. For walls, squeeze small amount of chocolate about 1/4 inch from each end of another pretzel. Lay pretzel across (and perpendicular to) 8 pretzels forming roof, about 1/4 inch from end. Repeat with another pretzel at other end of roof base. Squeeze small amounts of chocolate 1/4 inch from both ends of these two pretzels; place 2 more pretzels (perpendicular to last 2) in this chocolate. Repeat with 3 more pairs of pretzels (making all 4 walls from 12 pretzels total). Set aside until chocolate cools and sets, about 25 to 30 minutes. To serve, invert so roof is over walls.
Note
The chocolate will remain pliable for about an hour after melting. The more chocolate you use as glue, the better the cabins will hold together. Recipe may be doubled for larger classes.