It depends one who your laning against and how well you do in lane, but usually rushing a philostone is done when you get some early kills or assist. On your second buy you should just get a ruby crystal and at least 2 pink wards if not some regular sight ward. having bottom brush control is top priority for a support player because if your winning your lane you can zone them out and if your not you can at least have vision in it or use the pink ward defensively where your jungler can gank through. For most of the build as support ask your jungler whether he wants to grab a locket or aegis. Its not bad to have two aegis in the same team but its better if you don't build it at the same time, when you can get a locket on a jungler and an aegis on a support. Shurelia is also a good buy on lulu because she bring a lot of utility and having that shurelia increases the survivability of your teammate.