lol wow glad to hear someone tried to make one of these but um to answer any scaling questions.
i modeled all of these models with support strut for measuring so you get the right scale. so like with the helmet start at a reasonable height ,considerin 29 cm is the ODST helmet size, start somewhere around low 20's maybe less unless you have a hughe head lol no offense to anyone this applies to, then print out the page that the support strut that goes from the insed of the visor to the back of the neck and measure that. then give it a rough measure on yourself from the back of your neck right under the base of your cranium to pretty much your forehead a little above your eyebrows. do the math. the scale 29 is 1:1 so wat is the new scale going to be with the number of you put in after doing the math for the size of the strut.
lol that may have been a bit confusing but im sure ral partha can elaborate considering i got the idea from something he mentioned on the forums before