As of now there will be two promising solutions avilable right now to build your own marketplace using Drupal
(Based on Ubercart -The Drupal ecommerce module)
Ubercart is larger, and it remains strong and is not as flexible. However, this module can be customized for your use case exactly: Ubercart Marketplace-which is one of the Free Drupal Multi vendor module available in the market but the development has been stopped years back(Last known stable release is 03 Aug 2014)
And the another free Drupal marketplace module named Commerce-Marketplace is available which is competitively recently updated one(last known release is 18 April 2016).
You can choose between this according to your preferences(hyberlinks are given in the product names above)