Rodney

It sounds okay, but you really want to nail everything down in advance so nobody gets weird later because it didn't turn out the way they expected (but they didn't _tell_ anybody what they expected). But if what you can get everyone to agree to doesn't sound good to you, don't do it.

You should find out how many years your parents are okay with you staying there. Determine who's paying for major repairs -- if it needs a new roof, if the plumbing fails in a major way, if the heater needs replacing, etc. Think about what might happen if Mom & Dad die, or if there's a serious illness and they really need money. Will it be expected that you move out so that the house can be sold?

And if you add onto the house, who's paying for that? (And what do you get for the money or work you put in if they eventually sell the place.)

In short, get everyone's expectations in the same place -- yours, your parents, your brothers and sisters -- and you'll ensure family harmony down the line. I also would ask whether you really want to put money into an addition right now, if your job is to save. Could you get by with throwing a couple of storage units in the back yard to hold things that you don't have room for?