You'll save a few bucks if you buy parts and if you can post on a forum you can definitely follow instructions- it's no harder than building a lego set. Also the knowledge of it is good to have.
For example, here's that "Best" system in parts:
PCPartPicker part list / Price breakdown by merchant
Type
Item
Price
CPU
AMD - Ryzen 7 2700 3.2 GHz 8-Core Processor
$224.89 @ OutletPC
Motherboard
MSI - B450 TOMAHAWK ATX AM4 Motherboard
$114.88 @ OutletPC
Memory
Corsair - Vengeance LPX 16 GB (2 x 8 GB) DDR4-3000 Memory
$94.89 @ OutletPC
Storage
Crucial - MX500 500 GB M.2-2280 Solid State Drive
$62.95 @ Amazon
Storage
Seagate - Barracuda 2 TB 3.5" 7200RPM Internal Hard Drive
$59.78 @ OutletPC
Video Card
EVGA - GeForce RTX 2060 6 GB XC BLACK GAMING Video Card
$349.99 @ Amazon
Case
Fractal Design - Meshify C Dark TG ATX Mid Tower Case
$89.99 @ Amazon
Power Supply
Corsair - CXM 550 W 80+ Bronze Certified Semi-Modular ATX Power Supply
$59.89 @ OutletPC
Prices include shipping, taxes, rebates, and discounts
Total (before mail-in rebates)
$1097.26
Mail-in rebates
-$40.00
Total
$1057.26
Generated by PCPartPicker 2019-04-17 00:36 EDT-0400
You save 350-400$.
But considering you're just playing fortnite, you maybe need to spend ~900 for a higher end 1080p system like this:
PCPartPicker part list / Price breakdown by merchant
Type
Item
Price
CPU
AMD - Ryzen 5 2600 3.4 GHz 6-Core Processor
$164.89 @ OutletPC
Motherboard
MSI - B450 TOMAHAWK ATX AM4 Motherboard
$114.88 @ OutletPC
Memory
Corsair - Vengeance LPX 16 GB (2 x 8 GB) DDR4-3000 Memory
$94.89 @ OutletPC
Storage
Crucial - MX500 500 GB M.2-2280 Solid State Drive
$62.95 @ Amazon
Storage
Seagate - Barracuda 2 TB 3.5" 7200RPM Internal Hard Drive
$59.78 @ OutletPC
Video Card
Gigabyte - GeForce GTX 1660 6 GB GAMING OC Video Card
$229.99 @ Amazon
Case
Fractal Design - Meshify C Dark TG ATX Mid Tower Case
$89.99 @ Amazon
Power Supply
Corsair - CXM 550 W 80+ Bronze Certified Semi-Modular ATX Power Supply
$59.89 @ OutletPC
Prices include shipping, taxes, rebates, and discounts
Total (before mail-in rebates)
$917.26
Mail-in rebates
-$40.00
Total
$877.26
Generated by PCPartPicker 2019-04-17 00:37 EDT-0400