Most of the time when you are painting interior walls, you want to cut in around the edges with your brush and then immediately roll the open part of the wall so that the brushed part and the rolled part all dry together. In other words, you try to keep a "wet edge" between the cut-in and the rolled areas. Depending on the humidity, you can sometimes cut in an entire room before starting to use the roller, but most of the time you must cut in and then roll one wall at a time.
To prepare a galvanized roof for painting:
1. Insure that the roof is clean, preferably by pressure washing to remove, dirt, pollen, and tannic acid (if there are oak or pine trees nearby).
2. Scrape or sand to remove any loose rust or peeling paint.
A bathroom can provide a difficult environment for paint to perform as well as we would like for it to. A half bath without a shower or tub can be treated pretty much like any other room. Most of the time you would want to use a paint other than a flat just so that you have more washability. This could be as shiny as a gloss or as dull as an eggshell. This would depend more on personal preference than environmental demands. However, a shower and its accompanying steam and splashing create a much harsher environment for a coating to contend with.