The Dallas City Code is online, which saves you time in finding the general language of an ordinance.
However, if you need historical information you might want to try the 7th floor of the Dallas Public Library (Dallas History and Archives) or the 6th floor (Urban Information).
If your practice includes a lot of city ordinance work, you might want to consider owning a printed copy.
To reach the online version, use this URL.
Here you will find links to the various chapters.
City Code - Volumes 1 - 3
City Code - Volume 4 Chapter 51P is located at the City Attorney's website.
City Construction Code is located at the Building Inspection Site
City Council Rules of Procedure.