hello, i live in a large home
Oh really! So a mansion, then. Nice! Mansion actually comes from the Latin word for dwelling, so it's just a fancy way of saying home!
I wish it was a mansion just a big house
Honestly the definition isn't that strict. It really just means a place for a lord who remains there, so that could easily still be you!
then I am lord of my dwelling 
That's the spirit. And if you ever make the house bigger or add on to it anyway, its new considerable size could make it qualify as a palace!
are there specific sizes or is it more subjective on what to call it
Eh, mansion, palace, kingdom, castle, it's whatever makes you happiest, right? Whichever one hold the most significance for you. :)
so my next step is a palace :)
Yes indeed! Feeling aristocratic, wealthy, and luxurious is a state of mind. Fake it until you make it!