https://www.amazon.com/s/ref=nb_sb_ss_c_0_11?url=search-alias%3Daps&field-keywords=wilson+cell+phone+booster&sprefix=wilson+cell%2Caps%2C253 check these out.
What would be a good heat gun to purchase for use in the garage? I found this review on amazon, looks to be a good one http://www.amazon.com/review/R1VI5ZDP1ID56K/ref=cm_cr_dp_cmt?ie=UTF8&ASIN=B0025ZA76A&channel=detail-glance&nodeID=228013&store=hi#wasThisHelpful...
I don't know if it is the picture but it looks like the room above is sagging also. To be safe I too would recommend an engineer to have a look at it just to be safe.