I tried to create a cone in sheet metal environment but i wasn't successful.
there are several ways to do it, but the easiest is to use a "contour roll". create a sketch, draw a diagonal line some where to the right of the origin (make sure both end points are on the same side of the origin) put whatever dimensions and angles on it you need and finish the sketch. Set your thickness to whatever it needs to be in the "sheetmetal defaults" tab then select "contour roll from the sheet metal features menu. your diagonal line is the profile and whatever axis you want to revolve it around is your axis (I set mine up to use the Y-axis) then change your rolled angle to 365 degrees (i usually set mine to 359.9 so the seam will be visible) and click apply. inventor will make you rcone and add thickness on one side or another of your line depending on which of the direction buttons you had selected when you made the feature.
other ways to do it are to revolve a sketch profile around an axis or to loft one sketch to another (though i dont know why anyone would spend that much time trying to loft a cone).