malloryt, the only definition that you posted for "irregular rectangles" is "they are like two shapes in one".
That definition is inadequate.
I'm still thinking that you mean an irregular four-sided shape, like a rectangle with different triangles stuck on to one or more sides.
But, perhaps it's simpler than that. Maybe you mean shapes that are built solely from rectangles, by sticking different rectangles together.
Either way, calculating the perimeter is as easy as determining the lengths of all line sgements, distinguishing between line segments that are part of the perimeter versus not part of the perimeter, and adding the relevant segments together.
With area, you divide the shape up into smaller shapes whose area you can determine, and then add up all the sub-areas to get the total area.
In short, you need to decompose the shape into familiar objects, like rectangles, squares, and triangles. You know how to deal with those shapes.
And, most certainly, if you do not have a picture, draw one !