As long as you know the dimension of one thing within the drawing (the overall length of a wall, the width of a door, etc.) import it as you're doing and then just do an Enlargement (Edit/Enlarge/(set the center)/Enlargement/Cal. Dist.). If you're trying to do it when you import it you'll have to play around a little - it could be by a factor of 12, but then it could also be by a factor that is some wacky number too. With the Enlargement trick you have full control over what you're using as the control dimension.
Alan T. Hendry, RA
Intel i7-6700 (3.4GHz) Desktop, 32GB RAM, 3TB HD, Win 10 Pro 64-bit, DC 17, 18, 19, 20, 21 & 22 w/ latest beta
Intel i7-4702 (2.2GHz) Laptop, 16GB RAM, 1TB HD, Win 10 Pro 64-Bit, with DC 16 and all of the above