Really depends on your spans. There are load bearing charts that you can find on the net that will give you your maximum span, but IIRC itâs only about 9 foot for 40 pounds of weight with 2x4âs on 16â centers. Personally, I tend to over build, so Iâd shoot for a 60 pound weight anyway.
You canât go wrong spending a few bucks extra on the âbasicsâ, like the frame, foundation, plumbing and electrical of the house. Cheap out on stuff that is easy to change or upgrade later, like fixtures, windows, siding or the roofing. A solidly built house will last for centuries. A weakly built house only a few decades. Is 20% of the cost worth an extra 100 years? Iâd say so.
If you want to save on framing, find a sawmill that will sell you ârough cutâ lumber. It costs quite a bit less than kiln-dried lumber, around half as much. It is the standard lumber in most any home built before the 1950âs. The difficulty is that they are not âas standardâ as kiln dried wood. Youâll have to use furring strips to even out the frame before you can drywall. Strips cost about nothing, ($5 for a 40 pound bundle) itâs just a few days of extra work on an entire house.