Section 25. In addition to the duties imposed by the sixteenth and seventeenth sections of this act upon the commissioners named therein, they are hereby authorized to receive subscriptions of money and materials towards defraying the expenses of purchasing lots and erecting the public buildings of the county, and also to locate the seat of justice of said county: Provided however, That they shall be required to locate it at the place which will pay or secure to be paid the most money towards the erection of the public buildings of said county.