Building a shield

[Tarbicus]

I know that original roman shield were 120 cm long and 80 cm wide but the acient people were shorter than us right?

Yes they were, and well brought up. There definitely is a case for a lot of our kit being too small proportionally on our own bodies IMHO, including helmets (there is a difference in head sizes on races of a smaller stature before folks start shouting otherwise).

However, it's unlikely shields were of strict uniform size across the entire Empire or Republic anyway.