Here’s a set of instructions on how to build a variety of buildings for your colonial wargames.
There is no shortage of free wargames rules for the Colonial period. A good one is the Two Page Skirmish rules from Steve Winter.
Hordes of the Empire is a colonial variant of the Hordes of the Things rules. Hordes uses DBA mechanisms.
Empress Miniatures offers a set of free wargames rules called Damned Wobbly Gentlemen, designed for recreating battles of the Zulu War.
Death In The Desert is a set of free wargames rules for games involving the French Foreign Legion and bedouin Arabs.