It depends on how much data and how complicated.
You hit a functionality wall with MOLAP, which is very costly to get past with custom programming. ROLAP is easier to customize, mainly because SQL is a standard, and it's easy to find programmers who are good with it.
However, MOLAP is cheaper in terms of development time for basic stuff, especially in ETL and performance tuning. I don't know of any ROLAP tools that automatically produce the myriad of pre-calculated agg tables that MOLAP has by nature, or any ROLAP engine that can do member-wise selection or drill-down as quickly.
MOLAP's slightly cheaper because they bundle; ROLAP requires a database engine and a reporting engine. The box and disk are basically the same; if you need to customize these, you probably need ROLAP.