Unfortunately, Jagex lets us create rooms with no doors and doesn't let us doesn't let us move rooms once we've placed them without paying a second time. I'd like to have a web application that tells me where to place my rooms, which direction they should be, and let me view the setup before I spend a bunch of money making it for real in-game. Obviously, some rooms have more priority than others, like I'd want to place my gilded altar and oak larder training room as close as the portal as possible while I'd want to keep stupid rooms like the dining room and parlour in the far corners.

It would also be useful to have the tool display the highest level things we can make and how many planks/nails/etc we would need to max out our houses.

For what to make etc try this:

http://www.tip.it/runescape/?page=construction_calc.htm

For what to make etc try this:

http://www.tip.it/runescape/?page=construction_calc.htm

 

Or alternatively, http://www.tip.it/runescape/construction_table.php, which also shows the materials needed, though you'll still need to manually add up the totals needed for each material.

 

As for making something that's essentially a "house previewing tool", well, that sounds fairly challenging to make. I can see its use but it'll take a fair amount of time to make something that works. This is the first time I see this subject come up in a long time, so I'm not sure if it'll be worth it...

That's a good suggestion. Too bad I can't own a house... yet :-(

Looks like this has been dealt with then.