Lately it seems that most mansion builders have been sending their new mansions to the admins, asking them to do the beta testing.  While we love to do that it is impossible for us to test all mansions.  So when you have a mansion ready for beta testing please advertise it on boards (e.g. the Talk forum) and ask for volunteering beta testers instead of sending them to us.  When you and your beta testers think the mansion is ready for the final list you can sent it to us and we will put it on the final list.
While it is propably impossible to find all Jack stucks (JS) and cheap deaths (cd) in the testing period it is very important that all possible JS and cd that are found are fixed before a mansion is put  on the final list.  Take MM&M for instance, which is still being updated because players are still finding such things.  Always bear in mind that:
1. The majority of players does not want JS and cd and think it is unfair. The same applies to most players regarding forced deaths like having to kill a monster without a shield.  On the other hand it can be a challenge to find a shield to get past a monster.
2. Never ever assume that the player will play your mansion in the way you intended.  If there is a strange/stupid/whatever play that a player can do be sure that someone eventually will make that play. Remember that the player cannot know beforehand that the play will lead to JS or cd.

Builders are advised to use the building instructions that came with the game. You can find discussion about building tips and tricks here and here.