The assessor’s estimated value of some apartment buildings in the northern suburb have doubled or even tripled, fueling fears that a massive property tax increase is coming next year. Some spooked landlords predict they’ll have to hike rents to account for the higher costs. Others foresee a decline in property values and development as investors steer clear of the Chicago market. And don’t rule out a fight. Comment: we are routinely hearing about doubled or tripled residential assessments, too, in northern Cook County.