I understand that there are famous professional athletes with Crohn's. One of our doctors is permanently immune suppressed from complications from Crohn's - around sick people all day!
I think with construction, you get your disease under control with the meds, and just be very careful if you get cuts, scrapes, etc, from working. Clean everything out well! Once you are treated you may have more energy and feel better.
Also in the construction trades, if you are on jobs where you can set your pace, then you can take it easier on days where you are having a tougher time and maybe push to get the project done in the better moments. If there's only a roughed in bathroom on site....might be an issue.
How are your symptoms?