Compare and contrast an in-house Network design vs third party detwork design

a travel agency wants to know if it is cost effective to have their in-house IT team build a network that will replace their 5 regional call processing sites into a home-based virtual offices or is it better to have a third party build the network. the budget is 1.5 million for three years. this includes labor equipment and services. what equipment is needed. how does it work and cost. will performance, reliability, cost, and maintenance be different between in-house and third party equipment.