No, Trump's plans don't make sense. You can't build roads for free. Material needs to be purchased. Workers need to be paid. Where is the money going to come from? Roads cost money to build. Simple as that. There's no way to build them for free, unless he's going to use his own personal billions to fund roads (and of course, he won't).
How is the US going to get $1 trillion in roads for free? It seems that Trump would offer financial incentives to companies that build toll roads or other revenue producing infrastructure. On paper that sounds possible, business gets money from the government to build and pay employees, government recoups that in tolls. Not sure how sound that is in practice. In NJ our roads and bridges are in pretty bad shape. Government is spending taxpayer $$ to fix them and also charging us more in gas tax. Seems more likely to me that Trump's plan would do something similar.
Not much that Donald Trump says makes much sense. I feel like his whole presidential campaign started out as a joke that just went to far and he couldn't back out. If he is elected and doesn't listen to his advisers which he isn't likely to do because he is just so enormously arrogant. He thinks he knows it all and will just continue to drag out country into the gutter.
A constant in Trump's bid for president has been a lack of clear plans and policies. His platform is built on inciting fear and anger rather than economically sound ideas. He makes impassioned proclamations of grandiose ideas but cannot provide any evidence of what tangible steps he and his cabinet would take to make them a reality.