This paper presents an automatic line-drawing method designed for building images. The fast line segment detector with a false detection control and detects the outline and the door, or window edge features detected, which are used in the construction of edge tangent flow. Based on the modified ETF, the Difference-of-Gaussians is used to render the final line drawing styles. This scheme gives clear line features for building images without much noise, which is also simple and easy to implement. The test results verify the effectiveness of the presented algorithm.