depends what it is mate....if its a vehicle then get dimensions off the net...set your grid up in inches or TRUE measurement...METRIC!!....then you subdivide your gris to the required dimensions...for a car then make the wheels size need and the body just a block in the right size and use it as a template.
cheers bullet
bullet1968
"A Darkness at Sethanon", a book I aspire to model some of the charcters and scenes