Boolean operators are specific words used to combine keywords to improve the chances of finding relevant information. The most commonly used Boolean operators are AND, OR and NOT. Search results will contain both of the terms humour and therapy. Using AND decreases the number of results, because each time a keyword is added, the focus of the search is narrowed. Search results will contain one, or both, of the terms humour or laughter or comedy. Using OR increases the number of results, because a broader range of keywords is searched.
The actual cost of a flat roof depends on your location, the materials used, the complexity of the installation, and other factors. 1  Building a flat roof costs approximately $1.50 to $10.00 per square foot. 2  Assuming an average roof size of 1,500 square feet, that s a total cost of $2,250 to $15,000.
The following are figures for the average cost of roof replacement: 1  Asphalt: $700-$3,700. 2  Slate: $17,000-$84,000. 3  Wood shingles or shake: $7,000-$20,000.