Yesterday we found this wonderful mod by velocitygrass on Mod the Sims that allows us to make our own blueprints. While the instructions are pretty easy we thought it was good to show with screenshots how to make your own Blueprint!
1) Go to Mod the Sims, register an account and download the mod.
2) Extract the .package file to your mods folder and put the Blueprintmaker folder somewhere you can find it again. If you haven’t installed a .package file before, read our article on how to install Sims 3 downloads.
4) Build your room/studio. Currently you can extract one room at a time, so if you have an en-suite bathroom you will have to extract that separately.
6) Make sure you are in live mode and ctrl-click on the ground of the room you want to turn into a blueprint. Then choose velocitygrass > Create Blueprint Template with or without the outer wallpaper.
9) Then fill in the rest, make a pretty screenshot.11) Load your game and test your Blueprint!
Update) Make sure you click on the floor tiles directly and not on a rug. There seems to be a bug when the room does not export when clicking on a rug.
Remember that this mod is in its infancy right now, so you might experience bugs or errors with it. We recommend you report bugs to the maker of the mod in the modthesims thread, with as much detail as possible.