So this is coming a month late-

I'll assume you're referring to the eighteenth century, and to the line infantry. I will focus on the British army, as there is simply more readily available material on the subject published in English. The answer as regards issue and fitting is really both: uniforms were contracted for in bulk, and, once received, cut up and re sewn so as to fit each soldier individually. Tailors- which most regiments could boost more than a few of in their ranks- were detached to do the work. English author Bennet Cuthbertson recommended they be placed under guard, and we're not receive any extra pay for their trouble. The exact fitting of a soldier to his uniform was doubly essential- it added to the fine appearance of the battalion as a whole, and gave the individual private a pride in his appearance. This latter was a necessary prerequisite for transforming the awkward recruit into a professional soldier. Furthermore, there was an added practical dimension to the fitting of soldiers for their uniforms, which few modern authors have been willing to take into account. Though seemingly constricting, the construction of the coat allowed for full range of motion. The high placement of the armskyes prevented the coat from riding up upon the body, as seen in modern suit jackets. The closeness of the cuffs, which terminated at the joint of the wrist, prevented them from getting in the wash when performing the manual exercise.

For officers, matters were somewhat different. Though their clothing, from 1768 on, was regulated by the same warrant as that of the men, they had their uniforms made privately by military tailors. This should not be taken to mean that officers designed their own uniforms. Standing orders of the various British regiments provided instructions as to which tailor to visit for their regimentals. The tailors' pattern books provided details as to the various distinctions of each regiment and notes on military tailoring in general. Often, officers would go to a separate lace maker to have their coats trimmed after the regimental fashion and to receive their epaulettes. Additionally, officers would purchase any number of frock uniforms for everyday wear. Thomas Simes, another military author, recommended the purchase of two frock suits in addition to the dress regimentals.

I hope that answers your question- please let me know if you intended a different era or were referring to a different kind of soldier.