You'll be able to design indoors environments very accurately thanks to the measurement system integrated in Sweet Home 3D. Creating a room is as simple as dragging a pair of lines on a plain because the program will generate the 3D model automatically.
Don't worry about the doors or windows spaces because when using Sweet Home 3D will create that space when you'll place a window or a door on a certain wall.
Finally, the gallery of objects is vast and you can even add new ones if they are formatted as OBJ, LWS or 3DS.
Give it a try, remember, it´s totally free ad it can make you save a lot of money.