Using a mannequin could be a good idea for either the whole,most, or parts of an Android. Molding and casting is pretty crucial, I have found. Parts can be done in sections. Brush on silicone rubber or similar material can be found at smooth-on.com. Androids and robots generally consist of two main parts in whole:
1: main frame-skeletal structure (endoskeleton)
2: exoskeleton (includes skin/flashing)
To make a mold, consider the part you are going to use.
As for a mannequin, I will focus on an arm.
Step 1. Brush on silicone rubber (for urethane/liquid plastic casting) or pour in support box/frame to appropriate thickness. Let set.
Step 2. Apply a support shell out of plaster gauze, hard foam, plaster,etc. in halves. Let set.
Step 3. Divide/cut silicone rubber.
Step 4. Place entire mold back together with support shell and bind with ties or rubber bands.
Step 5. Mix liquid plastic/urethane (if pre-mixed pigment is desired)
Step 6. Pour into mold
Step 7. Slosh (or use plugs if specific thickness is crucial). Let set.
Note: hands can also be done using Alginate (but must cast fast, as alginate does not last long).