Pre-casted Concrete pad question

[Abu 3ali]

Dear Engineers

We would like to use precast concrete pads for the outdoor equipments (packaged and mini-split), the pre-casted pads will be placed on a (non-fixed) Tiles that are covering the roof waterproofing

so I need your suggestion and recommendation about that case. is it safe to use the pre-casted pads on a non-fixed tiles or will it make any problems ??

[install monkey]

http://www.tfsolutions.co.uk/product-range/pipe-support-and-frameworks/blocks/bbj-condensing-unit-blocks.html
or
http://www.bigfootsupport.com/
or
http://www.pumphousepumps.com/GroupInfo.aspx?Id=116
or if u prefer,concrete plinths will be fine