I have always built my cases as "Desktop's"....

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My reasoning has always been that heat rises to the top of the lid well away from all the individual components down below.
In a "Tower" case the PSU is generally at the top of the case, therefore all the heat generated by the CPU, GPU, etc, below, rise and add to the temperature of all the components above them in turn, including the the PSU at the top...

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My desktop is on the table in front of me which makes for easy access by just removing the lid, and it also keeps it well away from dust at floor level...

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(Extra fans fitted front and rear)...

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..geeez...that was a naff photo. I think my batteries are running down, (you will be pleased to know...

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Cheers all...

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Paul.
Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.