For a sniper, either Guns / Repair / Sneak or Energy Weapons / Science / Sneak. Don't try to blend the two, or at least wait until you've boosted your basic skills up. Stats is easy- 10 Int to start, 5's in everything else. Why? Skill points. Points make you, and getting 15 a level (17 with a perk) is a must. Worry about stats later; when it comes time to get stats, Strength and Agility are needed only in a minor role, maybe 7 points total. You need it to use the bigger firearms (read: Anti-Materiel Rifle) without experiencing a ton of scope wobble, and Agility to get access to some Guns related perks. Luck is your next big stat, get it to 10 ASAP. The reason for this is critical hits. Each point of luck is a 1% chance for a critical to happen. It doesn't seem like much, but there are perks that will boost your crit % by 5 points (15%) and equipment (NCR 1st Recon Beret) that add 5% (20%, or a 1 in 5 change to crit. Another perk will add 50% to all the damage your crits do (and remember, sneak attacks always crit) and weapons (Ratslayer and others) that multiply your odds of dealing a crit. This is important to a sniper style character because their weapons are usually slow to load and fire. Obviously you want to have some sort of backup weapon if nasties get too close; I highly advise the hunting shotgun for Guns characters and a plasma pistol or plasma defender for Energy Weapons users. Keep light armor on all the time (Reinforced Leather is probably best) due to the penalties that medium or heavy armor cause to the Sneak skill. Of course, having a suit of heavier armor is always advisable for when the MILK n COOKIES hits the fan.
An Explosives based character, on the other hand, should go Explosives / Science / <insert your favorite weapon skill here>. Same stats as before, but now you're more concerned with Perception. You'll come across dynamite early in the game, and plenty of it, so you aren't gimping your character early on. Get all the Explosives based perks you can- due to the rather expensive nature of ammo for these weapons, you want to make every shot count. Scrounger is a very useful perk for Explosives based characters too as it doubles the amount of ammo you find in containers. The build I did used Energy Weapons, just for the added explodey fun of the Meltdown perk. Throw the Bloody Mess perk in the mix and you're a gib factory.
As to what other perks you pick or what route you take, I leave that entirely up to the player.