Let me say from the start that I love pryramid (tee-pee) style tents. The major advantages are 1. Lightweight, 2. Large space & 3. Handle wind & snow very well.
As with all things, there are disadvantages; No vestibule for storage or to protect the interior from rain during entry & exit. IMHO, storage is not an issue due to the large space inside the tent. However, the pryramid design of the sloping doorway leaves the interior vulnerable to flash floods when entering or leaving during rainstorms.
I have come up with a solution that works in all but blowing storms. It has the three characteristics that I like; it's lightweight, it's cheap & it's easy. It does require the use of two trekking poles. (Not a problem for me, as my wife & I both use them anyway, one pair locked together for the main tent pole and the other pair for the "fly.")
I simply ordered 2 linear yards by 60" wide, sylnylon (1.1 oz.) and cut it into a triangle, 72" at the base & 60" high (measured perpendicular to the base. I hemmed the edges, reinforced the corners with a little leftover sylnylon and, sewed a couple of inches of crossgrain loop at each corner.
I then attach one corner to the loop at the top of the tent with a lightweight carabiner & attach the other 2 corners to trekking poles that each have a guyline & stake. I position the 2 poles to make a nearly equal sided triangle with the top of the tent, thereby providing a roof covering the doorway.
Setting the poles to their maximum length, allows plenty of room to duck under my triangular "fly" to enter the tent. You don't need to pull the guylines too tight as this would pull the top of the tent sideways.
The "fly" + 2 ti stakes & guylines all weigh 3 oz total. Since it is not a permanent modification, it can be left at home on sunny weekends. One word of caution, don't deploy it in blustery winds; (they don't call it a "fly" for nothing)! Nor do you want to use it in any significant snowfall.