I recently invaded a world that has a M.O.T.H.E.R. on it. As there are many artifact buildings on the planet, it is hard to figure out what the actual size is.

It might be worth having a little blue ? on artifact buildings saying the size it takes up since if you've never gotten the artifact to make the building, you don't know how much space it takes up.

Anyone want to tell me how big M.O.T.H.E.R. is?

If I remember well, MOTHER was 2 Space.

You could post all the structures here + total current size used and ask someone to help you count. (assuming you are willing to share your planet building configuration)

I'm not willing at the moment. Too new to know if I should be or not. However, it is an issue I can't believe I am the only one who is having. My guess is others have it but aren't here to ask.

Good call. but if there is any other specific structure size you have no idea which is preventing you from calculating the sizes, you can always check the wiki (though many spoilers are there too)
http://galaxylegion.com/wiki/index.php?title=Structures
http://galaxylegion.com/wiki/index.php?title=Special_Buildings_Info

Thanks for the links. I've done the math and it does take up two spaces. I've updated the wiki with what info I could get from having taken it from invasion. (IE, don't know if there is limit on how many per planet and/or how you get it.)

It's a limited time artifact during Mother's day.