Vestitus Romani
Togae
The formal garment of both the republic and the empire was the toga.  More
information on Roman garments may be found
here. Another good site on Roman
clothing is
here.  Like most things roman, the toga's form changed considerably
during the extent of the roman period.  Here are three of its forms (these are taken
from "The Roman Toga" by Lillian Wilson):
Arringatorre Toga (Early Republic)
The Arringatorre Toga of the Early Republic, the basic toga:
Large Republican Toga (1st century BC)
The Large Republican Toga of the time of Julius Caesar:
Ara Pacis Toga
The Toga of the Ara Pacis (early 1st century AD):
Making a Toga
First of all, start with the correct material.  The best choice is a light weight
wool flannel.  Do not use coat wool.  In Wilson's words, the material should
"have a moderate nap, so that the folds will tend to cling together".  In Wilson's
toga patterns the basic unit is defined as height of the wearer taken from the
base of the neck to the floor, with shoes on.  Girth is defined as the
circumference of the waist.  For each of these toga types the required
dimensions are:
Arringatorre
AB              Girth + 2 units
Aa and Bb    1/3 unit
CD              1 unit
cd                1 1/8 units

Large Republican
AB              Girth + 2 2/7 units
Aa and Bb    1/2 units
EF               1 1/8 units
CD              1 4/14 units
BO and AM  1/7 units
cd                1 1/2 units

Ara Pacis
AB               Girth + 2 1/3 units
Aa and Bb     1/8 unit
EF                1 2/7 units
CD               1 1/4 units
cd                1 13/18 units
cQ               2/3 units
dQ               1 1/18 units

The pattern and dimensions for the later Imperial Toga may be found
here.

The full appendix to Lillian Wilson's book may be found
here.  Pictures of her
toga reconstructions are also
here.

Folding the Toga
I have the large Republican toga (see below).  After quite a bit of effort I can
sometimes manage to put it on by myself.  The presence of a serva makes the
job signifcantly easier.  
Here is one site that explains the process.  The process
begins by drapping the toga over the left arm.  You then bring the material
around your back and under the right shoulder, drapping the end over your left
shoulder. The trick is getting the right amount of material drapped over your left
arm.  I never seem to get it right the first time. Take note that no pins are used.
Large Republican Toga