Left-click on the decision card, potential regions are shown in Green, prohibited ones in Red. Drag and drop the card onto the selected region, the costs are subtracted immediately.
I do not believe that you can build Roman Roads in the game, just improve regions that have no roads.
Most parts of the ancient world are essentially wilderness but the Romans were outstanding engineers and built roads to facilitate control. In the game, the Improve Roads regional decision allow you to place a track in a region that has none and so improve movement through it. It takes 12-turns to take effect, there's always a chance of failure but as I recall, if it works you get some of the Engagement Points spent back in your EP stock.
Road building is probably best thought of as a long-term strategic option.
There are no graphic changes to the map but the tool tip will advise you as to the state of the road net (None, Track, Roman Road) so you can tell where to play the decision card when planning.
< Message edited by Randomizer -- 12/21/2012 12:41:40 AM >