You are tasked with creating a function that calculates key envelope properties for a rectangular building. These properties are important in architectural design for understanding the building's exterior boundaries and surfaces. The function you need to write will take three measurements: the length, width, and height of the building. Using these, you will compute three values: the perimeter of the building's base, the total wall surface area (excluding the roof and floor), and the area of the roof.

First, consider the perimeter. For a rectangle, the perimeter is the sum of all four sides. In this case, the formula is 2 * (length + width). Next, the wall surface area includes the four vertical sides of the building, but not the roof or floor. Each pair of opposite walls has the same area: two walls are length x height and the other two are width x height. Add these together to get the total wall area: 2 * (length * height) + 2 * (width * height). Finally, the area of the roof is simply the area of the rectangle at the top of the building: length * width.

You will return these values in a dictionary with the keys 'perimeter', 'wall_area', and 'roof_area'. Each value should be a float or integer, depending on the input. This function will be useful for quickly assessing building envelope properties in various architectural calculations.