Building a PC inside a small form factor case is a whole new challenge compared to full-size and even mid-tower enclosures. It's also rewarding on multiple levels, one of those being a smaller footprint. If you're up for it, the Asus ROG Z11 Mini-ITX/DTX is an intriguing place to start, and it's on sale for $199.99 at Amazon.
That's $80 below its list price. You can save even more if you want to try your luck with a "Used - Like New" model that Amazon is offloading from its warehouse (it's an option on the product page). If you go that route, you can nab it for $172.49, saving yourself $107.50.
Let's get the strangeness of this PC case out of the way. Our friends at Tom's Hardware built a system inside the ROG Z11 and praised it for its aesthetics, and for the fact that it can be mounted vertically or horizontally, but noted it's cumbersome to access the rear I/O ports.
The other thing to consider is the type of motherboard that can fit into this case. It's built for mini-ITX and mini-DTX motherboards. So your motherboard choices are limited, though you can piece together a powerful PC based on either form factor these days.
Inside the case, the motherboard sits at an 11-degree angle. Asus designed it this way for better cooling—it leaves an additional 40mm of space behind the motherboard tray, which Asus says "enhances heat dissipation around the CPU and graphics card." KitGuru also looked at this case, and found that a vertical orientation provided the best cooling.
Other features include enough space to fit a three-slot graphics card, an ATX or SFX power supply unit, and either four 2.5-inch SSDs, or a 3.5-inch hard drive and two 2.5-inch SSDs.
This is not for everyone, but if you're looking to build a compact system with aggressive looks, it's worth consideration.
