To assemble a row-house you only need white glue and a careful hand. However, having a collection of Lego available for making jigs for ensuring square corners is very helpful.
To help keep track of parts, place each part from the polybag on to the parts diagrams. Extra diagrams are available at parts diagram 1 and parts diagram 2. (Note that there are extra parts that were part of the original design and no longer needed.)
The roof is supported by the two gable ends and by two internal rafters. Glue each rafter so that the rafter's peak aligns with the roof's top edge. (The top edge is the one with the notches for the chimneys.) The rafters are placed 1 1/4" from each side.
Finish off the chimneys with their tops. (This can be done when assembling the gable ends too.) Note that a couple of coats of white glue over the tops will help hide the seams.
Each floor is assembled in the same way. A front and a side are glued together.
Now glue the two front and side parts together and to the floor. I found it is best to apply a lot of glue to the edge of the floor and the edge of the walls and then push the walls to the floor. The perimeter tool is now used. It surrounds the walls and is angled upwards at a corner so as to apply equal pressure to each wall.
With the perimeter tool in place your hands are free to adjust the upper parts of the wall so that they align and are square. Again, corner jigs made with Lego are helpful.
Your row-house is will look like this at is point.
The reason why the floors were raised is to allow room for the alignment tabs. Add the alignment tabs to the second and third floors.
Add alignment tabs to the roof.
This is a slightly better design for this tool: