Knee length Tunics and Tunica were the most common item of clothing for Roman men, either linen in the summer and then wool, perhaps with a linen under-tunic, in the winter. Cloaks were also used and dependent on size could be utilised for a range of tasks.

Also, whilst the idea of Braccae (trousers) was originally considered to be both barbaric and masculine effeminate. However, moving into Northern Europe, especially the frontiers in places like Scotland meant that the Romans did quickly adopt the idea of trousers.

Edit: got masculine and effeminate mixed up. (thanks /u/Miles_Sine_Castrum