Question Summary:
Can an employee of an engineering firm design buildings that will be used for sinful activities?

Question Detail:

I am a civil engineer employed at a multi national consulting engineering company. I work as a structural engineer; my job entails structural design of buildings in general. Simply put, I need to ensure that the building is structurally sound and safe. Typically I calculate loads on different elements of the buildings (eg foundations, beams, columns etc) and design these elements accordingly.
My query is on the permissibily of working on projects as outlined in the scenarios below :
1. I have recently being asked by my manager to be involved in the design of a proposed new church. The church is still in pre conception stage, and I would be required to roughly calculate the loads and give an estimate of the sizes of different structural elements, as well provide some preliminary drawings to quantify these.
Should the structure go ahead, I would be required to do a detailed design of the structure as well as attend meetings and do site inspections.
Is it permissible for me to be involved in this design if:       
(i)  I have an option not to
(ii)  I am forced to do so and risk losing job if I don't
2. Consider the scenario above, except that the client is now:
(a) financial services group (eg sanlam, Alexander Forbes etc)
(b) an insurance company
(c)  the main use of the building will be for haram (eg gambling, betting, drinking etc)
What is the ruling for these?
3. For the above mentioned buildings /clients I were to be asked to help out by attending a single meeting or doing a once off design (ie not involved on a daily basis but only once off) will this be permitted?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
As a civil engineer in a consulting engineering company, the nature of your work is general and permissible in and of itself.
Therefore, it will be permissible for you to consult on behalf of your employer for a client who is building a church, a financial services firm, an insurance company, a place where alcohol is consumed, etc.
However, it will be safer and preferable to refrain from doing so out of precaution and taqwa. [i][ii][iii]
Mufti Sohail ibn Arif,
Assistant Mufti, Darul Iftaa
Chicago, USA
قوله وجاز تعمير كنيسة) قال في الخانية: ولو آجر نفسه ليعمل في الكنيسة ويعمرها لا بأس به لأنه لا معصية) [i]
 في عين العمل
رد المحتار، ٦/ ٣٩١
[ii] مسلم آجر نفسه من مجوسي ليوقد له النار لا بأس به. كذا في الخلاصة...ولو استأجر الذمي مسلما ليبني له
بيعة أو كنيسة جاز ويطيب له الأجر. كذا في المحيط.
الفتاوى الهندية، ٤/ ٤٥٠
[iii] فتاوى عثماني ٣/ ٣٩٥ -٣٩٦