I would be more comfortable in offering advice (or critiquing) a more completed model form. Window placement will be responsive to the entire volume including roof lines and adjacent surfaces.
The potential fenestration could be anything from strip to floor to ceiling to corner windows. The head may be arched, sloped, or straight. Which ever design scenario you engage will be impacted by the overall structural form.
OK…just noticed several layers were switched off. Now that I have turned them on, there are a number of scenarios that I could suggest, but I think your best bet would be to simply play with fenestration patterns that appeal to your aesthetic senses. You may consider setting frames in line with a window below or you may want to try extending an edge a reasonable distance beyond the edge of one of the windows on the main floor. In simple terms, you should experiment because much of design is exactly that. Just remember that realistically the total window area in a habitable room should be no less than roughly 10% of its net floor area.
It is usually a good idea to set the head height of all windows on the same level at about the same height above the floor line…say 6’-8" unless you are on the metric system (this promotes a sensible framing approach) or unless you intend to provide a clerestory window which occurs near the ceiling. You may also want to consider placement of skylights or dormers to allow more light into your loft.