I have kept shrapnel for last as even though it will help in getting good creeps dead, it is better that you get good aim and head shot for better harassing and survivability against enemy heroes. Also it will help in late games when enemies start to break down your tower as the minimum harass will keep them away until you can call your allies for help. But if you want you can keep shrapnel for first but just make sure that take aim and head shot is full before that :).
These Items will make sure that the enemy will stay away from you and now you are a big threat. But in my opinion daedalus and manta style arent really that required unless you get good kills and you have the money to get them. Desolator is really what will give you that push and with the incredible range of sniper , you can easily get kills while behind your teammates.
Now you can start to try and kill your enemy's without much fear as now with power boots and magic wand and shadow blade you will have extra life and a way to escape your enemy efficiently. But as make sure that you are with your teammates at all times.
= Most important thing to remember , is that to never be inffront of your teammates
as since sniper is a very squishy player, the enemy will come and just kill you fast, then even shadow blade cant help you. So always stay behind them and try to get kills
This is my first guide , it might be bad , if it is then plz comment on the improvements that can be done . THANK YOU.
Try not to get harassed too much. If possible take the mid lane other wise go into a lane with someone who has stun , slow , etc. Dont rush into a kill unless you can guarantee the kill , also when killing creep , just get the last kills. Your main aim of the early game would be to gain lots of gold and lvl up alot. Also if possible try to harass the enemy hero as much as you can but dont get killed!!.