It looks like the Lions have a $10 mil cap/dead cap number for Suh for next year regardless of whether Suh is re-signed. This evidently resulted from a couple of salary-for-signing-bonus swaps along the way in order to defer cap hit:
http://overthecap.com/player/ndamukong-suh/1816
So, while $27 mil is out of the question to start with, it's gets worse since tagging him at that amount would result in a $37 mil cap hit in 2015 with the $10 mil hangover.
The Lions have a $120 mil cap commitment already for next season including that $10 mil Suh number already on the books. Adding $27 mil would likely put them over the top with just that one player.
Then there's Detroit's other unrestricted free agents, 20 in all, including Fairly and two starting OL. They have 5 total DL who will be free agents.
The $10 mil Suh hangover for 2015 gives the Lions a significant incentive to get him signed to a long-term deal; taking that cap hit for a guy no longer on the roster is painful. They'll be looking to repeat the cap hit deferral process...a big signing bonus that can be spread over the term of the contract for cap purposes with low front end salary numbers.
The media kibitzing on this matter says Suh is likely to use Watt's 6 year / $100 mil deal as a benchmark in testing the free agent market. Even with a creatively structured deal, it doesn't look the Lions can swallow anything like that given the other free agents and the pre-existing 2015 commitments.
I'm sure many here will be pleased to know Detroit is officially entering cap purgatory. While not as bad as the 49er's cap hell ($153 mil in cap commitments already for next season), they shared the approach of loading up to get through a narrow win-now window. Some rebuilding must ensue.