That big storm that swept through central Arkansas during the pre dawn hours yesterday did more than just dampen the streets and blow down branches and leaves. At North Little Rock`s City Hall, officials found that blocked drains from a flat rooftop had resulted in flooding of the two story building. When the city`s youth services coordinator, Steve Nawojczyk (nah-VOY`-chek), opened up the building yesterday morning, he heard the sound of running water. He said the water was pouring like a waterfall down a marble stairway and out the front door onto Main Street. Officials said the blocked drains allowed about a foot of water to build up on the roof of the building, and it made its way down into the offices below. Among the second floor offices flooded was the one where Mayor Patrick Hayes works. He said he`ll have to move elsewhere while repairs are carried out. No estimate of the dollar amount of damages was available.