Good tools are absolutely not necessary, and the torque spec is there to prevent damage. You don't torque to the spec, you stop and fix the problem if it gets too high. It's NOT like tightening a lug nut.
If you are an experienced home auto repair owner, assembling an AR15 isn't rocket science, it's easy and less trouble than rebuilding a one barrel carburetor. Read the assembly stickies on arfcom and you will see the one time assembly of a single AR15 doesn't need a company armorer's kit that will disassemble and repair large crew served machine guns - also part of the job.
The current situation is that assembled guns are as cheap as the parts - since the Brand name builders buy in volume, they get lowers and uppers for less than $50 each. The overall savings buying in bulk is more than enough to cover assembly. CMMG Bargain Bin guns for $599 are a good example, compared to my cost of $950. And I only paid $75 for the lower, $48 for the upper, both stripped, and used an A1 stock and rifle handguard. I obviously didn't buy a discount $80 barrel, and all the hotrod BCM parts that really have no place on a hunting firearm.
Bargains can be had at a gunshow, but shopping online can beat it down quickly. Few would purchase a front sight base at a show for $120 when you can order one online for less than $30. Checking build forums for the bargains of the month can and will save money - if you check almost daily and have an idea of exactly how that part fits into the build philosophy.
Most getting into the AR build process miss the entire point: it's to make something you can't get otherwise, like a Colt 6920 in 6.8SPC. Specify exactly what you want it to do - target and range - then choose the caliber and barrel length that support the job. From there, add the upper needed, the furniture, and last, the trigger. Don't be surprised that when you are buying parts, the easiest thing to do is get a subkit that has all the little bits, and that the price ON THE DOORSTEP, shipping and discounts included, is what you really need to consider. I've bought most of my small parts as kits from Brownells because I get a significant military discount. My FSB now needs parts, too, almost done.
You don't want to be caught out ordering a firing pin retainer or sling swivel rivet - the front door cost shipped is nearly $10 for small single items. Shipping has already cost me over $45 on this build, which would pay for most of the linear compensator I chose. And that's the real issue of why building isn't cheap - upgrades from milspec are expensive, and often not in keeping with what the gun will really do. Since I built mine for hunting, I stuck with a GI charging handle and left off all the ambidextrous doodads.
Accessories get pricey, too, clamp on a set of BUIS, you pay over $85 for Magpul plastic, or $150 for iron. On the other hand, you can build with a GI FSB, and cut down a M4 carry handle for the rear, which used, only run $30-35. And milspec, too, and do the job.
Don't get caught up in a testosterone fueled exercise in marketing hype, and the basic decisions are made in a calm atmosphere - does the part actually contribute toward the job - Yes or No, not well maybe it will help in a 5% situation. Far too many build for the small chance what if situations and the result is something that's not the optimum combination for the 85% of the time they need the best. Hence all the pics of carbines with 3x9 variable scopes and bipods. Apparently some do shoot cockroaches in a maternity ward.
If what you want isn't really available, build, but be careful, and don't be surprised costs begin to add up. Otherwise, just buy and shoot it. It can be changed if needed, albeit not cheaply, as used parts never sell for a new price.