As with any answer about Rome, it depends on the time period since Rome spanned 1,000+ years. Early Roman soldiers had to supply themselves with arms and they were certainly not uniform because of this. Armies were actually striated based on the type of weapons each soldier could afford.

Later on, the Marian reforms were enacted to increase the base of citizenry available for military recruitment (this is 107BC). In order to do this, Marius did away with the strict property requirements for signing up to the army. This meant now a lot of poor citizens were eligible to sign up, and in order to recruit them the state began to provide equipment. So at this point the equipment would become more homogenised as almost all of it began to be supplied by the state.

Interestingly, at this point the creation of weaponry was managed by generals/military officials. This was seen by some later emperor's (post third century crisis) as having been one reason why rebellions had so readily popped up -if a senior military official was to rebel he would not only be in command of the army but also all the logistical support needed to supply them. During the Dominate (I forget which emperor specifically but I want to say Diocletian or maybe Constantine) began the process of splitting out the weapons factories to be part of the civil administration rather than being under the purview of the general, so that even if a general were to rebel and take his army with him it would be a lot more difficult to bring his weapons manufacturers with him as they would be taking orders from a totally separate command structure.

Source: Goldsworthy, The Fall of the West