I would argue an extension would probably be cheaper and less trauma if you plan to remain in the house, you are talking about removing the entire roof and building a new one above, not to mention all the internal work to do it and support it. This is where it's worth spending money on an Architect. There are more botched renovations and extensions when people plan them themselves, and an architect will have more answers for you than we will....but having not even seen your house, I'd say the extention would be easier. I don't imagine stairs are cheap, and you want them to be biggish (can you afford to lose that footprint in the existing house?) because, assuming you'll want a double bed or larger up there, it's a huge pain to get a bed up those add-on stairs which are often very small, or, worse still, spiral. I don't mind them but how do you get the furniture up there?

You shouldn't be measuring into a corner. Try along the path you would normally travel at a normal walking pace. And showing the bubble of a 4 ft level isn't particularly helpful either. You can probably find similar drops in the old house that you never notice. Walking in your socks along a straight path without looking at the floor is about the best way to judge if there is a problem. And I recommend waiting a month or two before doing it. With any luck you will forget to do it.

How did your bump out go? I have a similar problem, I have a very small full bath-it is only as wide as my bathtub and only as long as the stool, a wall-mounted sink, and the narrow end of the bath, with 12 inches or less separating each fixture--and would like a few more feet so I could add a walk-in shower and some kind of towel cubby. House is on a slab. If it is true that adding such a small bit of space is as expensive as adding 20/20 addition, then I guess I will continue to use the yucky shower head on the wall above the tub drain with a plastic shower curtain. Not ideal, but functional. :(

If the house has a good foundation, I would say go with it:) The decision is yours though. I have never built a house, but from what I have learned here, some of the less expensive builders limit choices - sometimes severely. There can be a choice of only a few cabinet styles and colors for the kitchen and only a few flooring choices etc. How much will it cost to get new hardwood and the good trim work your house may have? Maybe the inside is in very poor shape, but if there are well crafted elements, think about how much it would cost to replace them. If you go with what you have, you can work on it as you have funds and get what you want. If you think restore - except for the kitchen, your home will be cohesive, even if it takes several years. Are you far from Des Moines? You may have to go to a bigger city to get an architect. I am in Iowa and my countertop guy came a hundred miles to install my counters:) There are online resources for old homes: https://www.oldhouseonline.com/ https://www.oldhouseonline.com/articles/american-foursquare You can also look on Old House Dreams which has old houses for sale. Some are in bad shape, but some have been remodeled. You can filter the search (on the right hand side of the page) by picking "Prairie" because they don't have foursquare as a choice. Look online for forums and other sources for people who own and work on old houses. There are also bloggers working on old houses who blog about the experience. The most recent house being worked on in This Old House resembles a foursquare. The final wrap show is next weekend: https://www.thisoldhouse.com/watch/newton-generation-next-house My house is not nearly as old as yours and I did not have to redo plumbing and electrical. I did have to work on every room, some just cosmetic, some a bit more. Roof, windows, interior doors, floors, AC/heat - all had to be replaced. It was a run down renal when we moved in. I've liked not being limited by a builders choices of what I could do.